Displacement devices and methods for fabrication, use and control of same

ABSTRACT

Displacement devices comprise a stator and a moveable stage. The stator comprises a plurality of coils shaped to provide pluralities of generally linearly elongated coil traces in one or more layers. Layers of coils may overlap in the Z-direction. The moveable stage comprises a plurality of magnet arrays. Each magnet array may comprise a plurality of magnetization segments generally linearly elongated in a corresponding direction. Each magnetization segment has a magnetization direction generally orthogonal to the direction in which it is elongated and at least two of the magnetization directions are different from one another. One or more amplifiers may be connected to selectively drive current in the coil traces and to thereby effect relative movement between the stator and the moveable stage.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 14/354,515 having a 35 USC 371 date of 25 Apr. 2014 which is a national phase entry of PCT application No. PCT/CA2012/050751 having an international filing date of 22 Oct. 2012 which claims the benefit of the priority of U.S. application No. 61/551,953 filed 27 Oct. 2011 and of U.S. application No. 61/694,776 filed 30 Aug. 2012. All of the prior applications in referred to in this paragraph are hereby incorporated herein by reference.

TECHNICAL FIELD

The invention relates to displacement devices. Particular non-limiting embodiments provide displacement devices for use in the semiconductor fabrication industry.

BACKGROUND

Motion stages (XY tables and rotary tables) are widely used in various manufacturing, inspection and assembling processes. A common solution currently in use achieves XY motion by stacking two linear stages (i.e. a X-stage and a Y-stage) together via connecting bearings.

A more desirable solution involves having a single moving stage capable of XY motion, eliminating additional bearings. It might also be desirable for such a moving stage to be able to provide at least some Z motion. Attempts have been made to design such displacement devices using the interaction between current-carrying coils and permanent magnets. Examples of efforts in this regard include the following: U.S. Pat. No. 6,003,230; U.S. Pat. No. 6,097,114; U.S. Pat. No. 6,208,045; U.S. Pat. No. 6,441,514; U.S. Pat. No. 6,847,134; U.S. Pat. No. 6,987,335; U.S. Pat. No. 7,436,135; U.S. Pat. No. 7,948,122; US patent publication No. 2008/0203828; W. J. Kim and D. L. Trumper, High-precision magnetic levitation stage for photolithography. Precision Eng. 22 2 (1998), pp. 66-77; D. L. Trumper, et al, “Magnet arrays for synchronous machines”, IEEE Industry Applications Society Annual Meeting, vol. 1, pp. 9-18, 1993; and J. W. Jansen, C. M. M. van Lierop, E. A. Lomonova, A. J. A. Vandenput, “Magnetically Levitated Planar Actuator with Moving Magnets”, IEEE Tran. Ind. App., Vol 44, No 4, 2008.

There is a general desire to provide displacement devices having characteristics that improve upon those known in the prior art.

The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.

FIG. 1A is a partial schematic isometric view of a displacement device according to a particular embodiment of the invention.

FIG. 1B is a partial schematic cross-sectional view of the FIG. 1A displacement device along the line 1B-1B.

FIG. 1C is a partial schematic cross-sectional view of the FIG. 1A displacement device along the line 1C-1C.

FIG. 1D shows additional detail of one of the Y-magnet arrays of the FIG. 1A displacement device in accordance with a particular embodiment.

FIG. 1E shows additional detail of one of the X-magnet arrays of the FIG. 1A displacement device in accordance with a particular embodiment.

FIG. 2 is a schematic partial cross-sectional view of a single layer of coil traces which may be used in the FIG. 1 displacement devices and which are useful for showing a number of coil parameters.

FIGS. 3A-3F are schematic partial cross-sectional views of single layers of coil traces having different layouts which may be used in the FIG. 1 displacement device.

FIGS. 4A and 4B are schematic partial cross-sectional views of multiple layers of coil traces having different layouts which may be used in the FIG. 1 displacement device.

FIG. 5 is a schematic partial view of a single layer of coil traces showing a group connection scheme which may be used in the FIG. 1 displacement device.

FIGS. 6A and 6B are schematic partial cross-sectional views of layouts of magnet arrays which may be used in the FIG. 1 displacement device and which are useful for showing a number of magnet array parameters.

FIGS. 7A-7L show additional details of magnet arrays suitable for use with the FIG. 1 displacement device in accordance with particular embodiments.

FIGS. 8A-8L show additional details of magnet arrays suitable for use with the FIG. 1 displacement device in accordance with particular embodiments.

FIGS. 9A and 9B are schematic cross-sectional views of pairs of parallel adjacent magnet arrays according to particular embodiments suitable for use with the FIG. 1 displacement device and showing the magnetization directions of their corresponding magnetization segments.

FIGS. 10A-10D are schematic cross-sectional views of layouts of magnet arrays which may be used in the FIG. 1 displacement device in accordance with other embodiments.

FIGS. 11A-11C are schematic cross-sectional views of magnet arrays and coil traces used to demonstrate a theoretical field folding principle.

FIG. 11D is a schematic cross-sectional view showing one layer of coil traces and a single magnet array that may be used in the FIG. 1 displacement device and how the field folding principle of FIGS. 11A-11C may be used in practice.

FIG. 12 is a schematic cross-sectional view showing one layer of coil traces and a single magnet array which are useful for describing the determination of current commutation.

FIGS. 13A and 13B schematically depict an assumed magnet array configuration which can be used to determine suitable currents for magnet arrays having non-magnetic spacers.

FIG. 14A schematically illustrates one embodiment of a sensing system suitable for use with the FIG. 1 displacement device for separately measuring the positions of the moveable stage and stator relative to a metrology frame. FIGS. 14B and 14C schematically illustrate other embodiments of sensor systems suitable for use with the FIG. 1 displacement device.

FIG. 15 shows a schematic block diagram of a control system suitable for use in controlling the FIG. 1 displacement device.

FIGS. 16A-16D schematically depict a technique for interchanging moveable stages between multiple stators according to one embodiment of the invention.

FIG. 17A schematically depicts a technique for interchanging moveable stages between multiple stators according to another embodiment of the invention. FIG. 17B schematically depicts how two moveable stages can be controlled with six degrees of freedom on one stator.

FIG. 18 schematically illustrates an apparatus for moving a plurality of moveable stages through a plurality of different stages.

FIG. 19A is a horizontal cross-sectional view of a rotary displacement device according to an embodiment of the invention. FIGS. 19B and 19C respectively depict a bottom cross-sectional view of the moveable stage (rotor) of the FIG. 19A displacement device and a top view of the stator of the FIG. 19A displacement device.

FIG. 19D is a bottom cross-sectional view of a moveable stage (rotor) according to another embodiment which may be used with the FIG. 19A displacement device.

FIG. 19E is a top view of a stator according to another embodiment which may be used with the FIG. 19A displacement device.

FIGS. 20A-20C schematically depict displacement devices according to other embodiments having different relative orientations of coil traces and magnet arrays.

FIGS. 21A-21C schematically depict cross-sectional views of magnet arrays having different numbers of magnetization directions within a particular magnetic spatial period.

FIG. 22A shows a coil trace layout according to another embodiment which may be used in the FIG. 1 displacement device. FIG. 22B illustrates a pair of adjacent layers of Y-oriented coil traces which may be used in the FIG. 1 displacement device.

FIGS. 23A-23F show a number of Y-oriented coil traces which (while generally linearly elongated in the Y-direction) exhibit periodic spatial variation which extends in the X-direction over their respective Y-dimensions and which may be used in the FIG. 1 displacement device.

FIGS. 24A and 24B show a pair of Y-oriented coil traces which have periodic variation which may be superposed to provide the Y-oriented coil trace of FIG. 24C.

FIGS. 25A-25D show various embodiments of magnet arrays having offset or shifted sub-arrays which may be used in the FIG. 1 displacement device.

FIGS. 26A, 26B and 26C show a number of Y-magnet arrays which exhibit periodic spatial variation which extends in the X-direction over their respective Y-dimensions and which may be used in the FIG. 1 displacement device.

FIGS. 27A and 27B respectively depict a top view of a number of coil traces and a cross-sectional view of a coil trace which comprise multiple sub-traces in accordance with a particular embodiment which may be used in the FIG. 1 displacement device.

FIGS. 28A and 28B show various views of circular cross-section coil traces according to another embodiment which may be used with the FIG. 1 displacement device. FIGS. 28C and 28D show embodiments of how coil traces may comprise multiple sub-traces having circular cross-section.

DESCRIPTION

Throughout the following description specific details are set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense.

Displacement devices are provided which comprise a stator and a moveable stage. The stator comprises a plurality of coils shaped to provide pluralities of generally linearly elongated coil traces in one or more layers. Layers of coils may overlap in the Z-direction. The moveable stage comprises a plurality of magnet arrays. Each magnet array may comprise a plurality of magnetization segments generally linearly elongated in a corresponding direction. Each magnetization segment has a magnetization direction generally orthogonal to the direction in which it is elongated and at least two of the of the magnetization directions are different from one another. One or more amplifiers may be selectively connected to drive current in the coil traces and to thereby effect relative movement between the stator and the moveable stage.

Particular Embodiment

FIG. 1A is a partial schematic isometric view of a displacement device 100 according to a particular embodiment of the invention. FIGS. 1B and 1C are partial schematic cross-sectional views of displacement device 100 along the lines 1B-1B and 1C-1C respectively. Displacement device 100 comprises a moveable stage 110 and a stator stage 120. Moveable stage 110 comprises a plurality (e.g. 4 in the illustrated embodiment) of arrays of permanent magnets 112A, 112B, 112C, 112D (collectively, magnet arrays 112). Stator stage 120 comprises a plurality of coils 122. As explained in more detail below, each of coils 122 is elongated along a particular dimension, such that in a working region 124 of stator 120 (i.e. a region of stator 120 over which moving stage 110 can move), coils 122 effectively provide linearly elongated coil traces 126. As explained in more detail below, each of coil traces 126 comprises a corresponding axis along which it is linearly elongated. For clarity, only a portion of the working area 124 of stator 120 is shown in the views of FIGS. 1A-1C. It will be appreciated that outside of the partial views of FIGS. 1A-1C, coils 122 have loops which are not linearly elongated. The loops of coils 122 are located sufficiently far outside of the working area 124 of stator 120 that these loops do not have an impact on the operation of device 100.

In the illustrated embodiment (as best seen in FIG. 1C), stator 120 comprises a plurality (e.g. 4 in the illustrated embodiment) of layers 128A, 128B, 128C, 128D (collectively, layers 128) of coil traces 126, with each pair of coil trace layers 128 separated from one another by an electrically insulating layer 130. It will be appreciated that the number of layers 128 in stator 120 may be varied for particular implementations and that the number of layers 128 shown in the illustrated embodiment is convenient for the purposes of explanation. In the illustrated embodiment, each layer 128 comprises coil traces 126 that are linearly elongated along axes that are parallel to one another. In the case of the illustrated embodiment, layers 128A, 128C comprise coil traces 126Y which are generally linearly elongated in directions parallel to the Y-axis and layers 128B, 128D comprise coil traces 126X which are generally linearly oriented in directions parallel to the X-axis. Coil traces 126Y which are generally linearly oriented along the Y-axis may be referred to herein as “Y-coils” or “Y-traces” and, as explained in more detail below, may be used to move moveable stage 110 in the X and Z directions. Similarly, coil traces 126X which are generally linearly oriented along the X-axis may be referred to herein as “X-coils” or “X-traces” and, as explained in more detail below, may be used to move moveable stage 110 in the Y and Z directions.

In the illustrated embodiment (as shown best in FIG. 1B), moveable stage 110 comprises four magnet arrays 112. In some embodiments, moveable stage 110 may comprise more than four magnet arrays 112. Each magnet array 112A, 112B, 112C, 112D comprises a plurality of corresponding magnetization segments 114A, 114B, 114C, 114D (collectively, magnetization segments 114) having different magnetization directions. In the illustrated embodiment, each magnetization segment 114 is generally elongated along a corresponding axial dimension. The elongated shape of magnetization segments 114 of the illustrated embodiment is shown best in FIG. 1B. It can be seen that in the case of the illustrated embodiment, magnetization segments 114A of magnet array 112A and magnetization segments 114C of magnet array 112C are generally elongated in directions parallel to the X-axis and magnetization segments 114B of magnet array 112B and magnetization segments 114D of magnet array 112D are generally elongated in directions parallel to the Y-axis. Because of the direction of elongation of their respective magnetization segments 114: magnet arrays 112A, 112C may be referred to herein as “X-magnet arrays” 112A, 112C and their corresponding magnetization segments 114A, 114C may be referred to herein as “X-magnetization segments”; and magnet arrays 112B, 112D may be referred to herein as “Y-magnet arrays” 112B, 112D and their corresponding magnetization segments 114B, 114D may be referred to herein as “Y-magnetization segments”.

FIG. 1C schematically shows the orientation of the magnetization of the various magnetization segments 114B of Y-magnet array 112B in accordance with a particular non-limiting example. More particularly, the schematically illustrated arrows in Y-magnet array 112B of FIG. 1C show the magnetization directions of the various magnetization segments 114B. Also, within each magnetization segment 114B, the shaded regions represent the north poles of the magnets and the white regions represent the south poles of the magnets.

FIG. 1D shows a cross-sectional view of Y-magnet array 112B in more detail. It can be seen that Y-magnet array 112B is divided into a number of magnetization segments 114B along the X-axis and that the magnetization directions of the various segments 114B are oriented in directions orthogonal to the Y-axis—i.e. the magnetization directions of the magnetization segments 114B are orthogonal to the Y-axis direction along which magnetization segments 114B are elongated. It may also be observed from FIG. 1D that the magnetization directions of magnetization segments 114B have a spatial periodicity with a period (or wavelength) λ, along the X-axis. This spatial periodicity λ of the magnetization directions of the magnetization segments 114 of a magnet array 112 may be referred to herein as the magnetic period λ, magnetic spatial period λ, magnetic wavelength λ or magnetic spatial wavelength λ.

In the illustrated FIG. 1D embodiment, Y-magnet array 112B has a total X-axis width of 2λ—i.e. two periods of the magnetic period λ. This is not necessary. In some embodiments, Y-magnet array 112B has a total X-axis width W_(m) given by W_(m)=N_(m)λ. where N_(m) is a positive integer.

In the case of the illustrated FIG. 1D embodiment, magnetization segments 114B comprise four different magnetization directions: +Z, −Z, +X, −X which together provide a magnetic spatial period λ. This is not necessary. In some embodiments, magnetization segments 114B may comprise as few as two magnetization directions to provide a magnetic spatial period λ and in some embodiments, magnetization segments 114B may comprise more than four magnetization directions to provide a magnetic spatial period λ. The number of different magnetization directions of a magnet array 112 that make up a complete spatial magnetic period λ may be referred to herein as N_(t). Regardless of the number N_(t) of magnetization directions of magnetization segments 114B, the magnetization direction of each segment 114B is oriented generally orthogonally to the Y-axis. FIG. 1D also shows that, in the illustrated embodiment, the X-axis width of a magnetization segment 114B is either: λ/(2 Nt) or λ/N_(t). In the case of the FIG. 1D embodiment, where the number N_(t) of magnetization directions is N_(t)=4, the X-axis width of magnetization sections 114B is either λ/8 (as is the case for the edge segments labeled A, I) or λ/4 (as is the case for the interior segments labeled B,C,D,E,F,G,H).

Another observation that may be made in the case of the illustrated FIG. 1D embodiment is that the magnetization of magnetization segments 114B is mirror symmetric about a central Y-Z plane 118 (i.e. a plane 118 that extends in the Y-axis and Z-axis directions and that intersects magnet array 112B at the center of its X-axis dimension). While not explicitly shown in FIG. 1D, in some embodiments magnet array 112B may be provided with a non-magnetic spacer at the center of its X-axis dimension. More particularly, magnetization segment 114B at the center of the X-axis dimension of magnet array 112B (i.e. the segment labeled E in the illustrated embodiment) may be divided into two segments of width λ/(2 Nt)=λ/8 and a non-magnetic spacer may be inserted therebetween. As explained in more detail below, such a non-magnetic spacer can be used to cancel disturbance forces/torques generated by higher order magnetic fields. Even with such non-magnetic spacer, magnet array 112B and its magnetization segments 114B will still exhibit the properties that: that the magnetization directions of the various segments 114B are oriented in directions orthogonal to the Y-axis; the X-axis widths of the various segments 114B will be either: λ(2 Nt) (for the outer segments A,I and the two segments formed by dividing segment E) or λ/Nt (for the interior segments B,C,D,F,G,H); and the magnetization of magnetization segments 114B is mirror symmetric about central Y-Z plane 118.

Other than for its location on moveable stage 110, the characteristics of Y-magnet array 112D and its magnetization segments 114D may be similar to those of Y-magnet array 112B and its magnetization segments 114B.

FIG. 1E shows a cross-sectional view of X-magnet array 112A in more detail. It will be appreciated that X-magnet array 112A is divided, along the Y-axis, into a number of magnetization segments 114A which are generally linearly elongated in the X-axis direction. In the illustrated embodiment, the characteristics of X-magnet array 112A and its magnetization segments 114A may be similar to those of Y-magnet array 112B and its magnetization segments 114B, except that the X and Y directions are swapped. For example, the magnetization directions of magnetization segments 114A have a spatial periodicity with a period (or wavelength) λ along the Y-axis; the width W_(m) of X-magnet array 112A in the Y-direction is given by W_(m)=N_(m)λ. where N_(m) is a positive integer; the magnetization directions of the various magnetization segments 114A are oriented in directions orthogonal to the X-axis; the Y-axis widths of the various magnetization segments 114A are either: λ/(2 N_(t)) (for the outer segments A,I) or λ/N_(t) (for the interior segments B,C,D,E,F,G,H), where λ_(t) represents the number of different magnetization directions in magnet array 112A; and the magnetization of magnetization segments 114A is mirror symmetric about central X-Z plane 118.

Other than for its location on moveable stage 110, the characteristics of X-magnet array 112C and its magnetization segments 114C may be similar to those of X-magnet array 112A and its magnetization segments 114A.

Referring to FIGS. 1B and 1C, the operation of displacement device 100 is now explained. FIG. 1C shows how moveable stage 110 is spaced upwardly apart from stator 120 in the Z-direction. This space between stator 120 and moveable stage 110 can be maintained (at least in part) by Z-direction forces created by the interaction of coils 122 on stator 120 with magnet arrays 112 on moveable stage 110 as discussed below. In some embodiments, this space between stator 120 and moveable stage 110 can be maintained using additional lifting and/or hoisting magnets, aerostatic bearings, roller bearings and/or the like (not shown), as is known in the art.

FIG. 1B shows four sets of active coil traces 132A, 132B, 132C, 132D (collectively, coil traces 132), each of which (when carrying current) is primarily responsible for interacting with a corresponding one of magnet arrays 112A, 112B, 112C, 112D to impart forces which cause moveable stage 110 to move. More particularly: when coil traces 132A are carrying current, they interact with X-magnet array 112A to impart forces on moveable stage 110 in the Y and Z directions; when coil traces 132B are carrying current, they interact with Y-magnet array 112B to impart forces on moveable stage 110 in the X and Z directions; when coil traces 132C are carrying current, they interact with X-magnet array 112C to impart forces on moveable stage 110 in the Y and Z directions; and when coil traces 132D are carrying current, they interact with Y-magnet array 112D to impart forces on moveable stage 110 in the X and Z directions.

It will be appreciated that coil traces 132 shown in FIG. 1B can be selectively activated to impart desired forces on moveable stage 110 and to thereby control the movement of moveable stage 110 with six degrees of freedom relating to the rigid body motion of moveable stage 110. As explained further below, coil traces 132 can also be controllably activated to control some flexible mode vibrating motion of moveable stage 110. When moveable stage 110 is shown in the particular position shown in FIG. 1B, coil traces other than coil traces 132 may be inactive. However, it will be appreciated that as moveable stage 110 moves relative to stator 120, different groups of coil traces will be selected to be active and to impart desired forces on moveable stage 110.

It may be observed that the active coil traces 132 shown in FIG. 1B appear to interact with other magnet arrays. For example, when carrying current, coil traces 132C interact with X-magnet array 112C as discussed above, but coil traces 132C also pass under a portion of Y-magnet array 112B. One might expect that, the current in coil traces 132C might interact with the magnets in Y-magnet array 112B and impart additional forces on moveable stage 110. However, because of the aforementioned characteristics of Y-magnet array 112B, the forces that might have been caused by the interaction of coil traces 132C and the magnetization segments 114B of Y-magnet array 112B cancel one another out, such that these parasitic coupling forces are eliminated or kept to a minimal level. More particularly, the characteristics of Y-magnet array 112B that eliminate or reduce these cross-coupling forces include: Y-magnet array 112B includes magnetization segments which are generally elongated in the Y-direction with varying magnetizations which are oriented orthogonally to the Y-direction; the X-dimension width Wm of Y-magnet array 112B is Wm=Nmλ, where Nm is an integer and λ, is the magnetic period λ, described above; and Y-magnet array 112B is mirror symmetric about a Y-Z plane that runs through the center of the X-dimension of Y-magnet array 112B.

For example, the X-dimension width Wm of Y-magnet array 112B being an integer number of magnetic wavelengths (Wm=Nmλ) minimizes force coupling with non-aligned coil traces 132C, because the net force on magnet array 112B will integrate to zero (i.e. will cancel itself out) over each wavelength λ of magnet array 112B. Also, the mirror-symmetry of Y-magnet array 112B about a Y-Z plane that is orthogonal to the X-axis and runs through the center of the X-dimension of Y-magnet array 112B minimizes the net moment (about the Z-axis and about the Y-axis) due to the interaction of magnet array 112B with X-oriented coil traces 132C. Similar characteristics of Y-magnet array 112D eliminate or minimize cross-coupling from coil traces 132A.

In an analogous manner, the characteristics of X-magnet array 112A eliminate or reduce cross-coupling forces from coil traces 132B. Such characteristics of X-magnet array 112A include: X-magnet array 112A includes magnetization segments which are generally elongated in the X-direction with varying magnetizations which are oriented orthogonally to the X-direction; the Y-dimension width Wm of X-magnet array 112A is Wm=Nmλ, where Nm is an integer and λ is the magnetic period λ described above; and X-magnet array 112A is mirror symmetric about a X-Z plane that is orthogonal to the y-axis and runs though the center of the Y-dimension of X-magnet array 112A. Similar characteristics of X-magnet array 112C eliminate or minimize cross coupling from coil traces 132D.

Coil Array

Additional detail of stator 120 and its coil arrays is now provided. As described above, stator 120 comprises a plurality of layers 128 of coil traces 126 which are generally linearly oriented in the working region 124. Each layer 128 comprises coil traces 126 that are generally aligned with one another (e.g. generally linearly elongated in the same direction). In the illustrated embodiment of FIGS. 1A-1E, vertically adjacent layers 128 (i.e. layers 128 next to one another in the Z-direction) comprise coil traces 126 that are orthogonally oriented with respect to one another. For example, coil traces 126Y in layers 128A, 128C (FIG. 1C) are generally linearly oriented parallel to the Y-axis and coil traces 126X in layers 128B, 128D are generally linearly oriented parallel to the X-axis. It will be appreciated that the number of layers 128 of coil traces 126 in stator 120 need not be limited to the four traces shown in the illustrated embodiment. In general, stator 120 may comprise any suitable number of layers 128 of coil traces 126. Further, it is not a requirement that the orientations of coil traces 126 in vertically adjacent layers 128 be different from one another. Some embodiments may comprise a number of vertically adjacent layers 128 of Y-oriented traces 126Y followed by a number of vertically adjacent layers 128 of X-oriented coil traces 126X.

Stator 120 and its arrays of coils 122 may be fabricated using one or more printed-circuit boards (PCBs). PCBs can be manufactured using standard PCB fabrication, flat-panel display lithography, lithography and/or similar technology known in the art to provide coils 122 and coil traces 126. Insulator layers 130 (such as FR4 core, prepreg, ceramic material and/or the like) may be fabricated or otherwise inserted between coil layers 128. One or more coil layers 128 may be stacked together (i.e. in the Z-direction) in a single PCB board. In some embodiments, coil traces 126 generally elongated in the same direction (at different layers 128) may be connected in parallel or serially, depending on via design and/or connecting methods for the ends of coil traces 126. In some embodiments, coil traces 126 generally elongated in the same direction (at different layers 128) are not connected to one another.

Coils 122 fabricated using PCB technology can accommodate sufficient current for controlling the motion of moveable stage 110. By way of non-limiting example, each coil 122 can be made from 6 oz copper (about 200-220 μm thick) or more. As discussed above, in active region 124, each coil 122 is in the shape of a flat strip or coil trace 126, which provides good thermal conductivity due to the high ratio of surface area to volume. The inventors have confirmed (via testing) that laminated copper can carry a sustained current density of 10 A/mm² with a 50° C. temperature rise above ambient without using an active heat sink. Another advantage of planar layers 128 of coils 122 and coil traces 126 is that the naturally stratified conductors that provide coils 122 make them ideally suitable for carrying AC current, because the self-generated alternating magnetic field can easily penetrate the conductor through top and bottom surfaces but generates only low self-induced eddy currents.

Multiple PCBs may be aligned side by side in both X and Y directions (similar to floor tiles) to provide the desired X-Y dimensions for active region 124. Board-to-board lateral connections (in the X and/or Y directions) may be made at the edges by connecting pads, through-holes of edge-adjacent boards, copper wires and/or using other suitable bridging components of the like for electrically connecting conductors on adjacent PCB boards. In some embodiments, such bridging components may be located underneath the PCB boards (e.g. on the side opposite moveable stage 110); in some embodiments, such bridging components may be additionally or alternatively located above the PCB boards or on the side(s) of the PCB boards. When PCBs are connected adjacent to one another in the X and/or Y directions, the end terminals (not shown) of coils 122 may be located at or near the perimeter of stator 120 for ease of wiring to the drive electronics. Connecting PCBs to one another in this manner allows displacement device 100 to be easily extended in both X and Y dimensions for various applications. When PCBs are connected to one another in the X and/or Y dimensions, the total number of coils 122 increases linearly with the X-Y dimensions of active area 124 of stator 120 (instead of quadratically, as is the case in some prior art techniques involving so-called “racetrack” coil designs). In some embodiments, coil traces 126 on X-Y adjacent PCB boards may be serially connected to one another to reduce the number of amplifiers (not shown) for driving current through coil traces 126. In some embodiments, coil traces 126 on X-Y adjacent PCB boards may be individually controlled by separate amplifiers to increase the flexibility for multi-stage actuation and to reduce heat generation.

A single PCB board may be fabricated to have a thickness (in the Z-direction) of up to 5 mm (or more) using available PCB technology. When thicker boards are required for heavy-duty applications, multiple PCBs can be stacked vertically in the Z direction. Another benefit of using PCB technology to fabricate stator 120 is the possibility of deploying large numbers of low-profile sensors (such as Hall-effect position sensor, capacitive position sensors and/or the like) directly on the board using daisy chain connections.

FIG. 2 is a schematic partial cross-sectional view of a single layer 128 of stator 120 and its coil traces 126 which may be used in the FIG. 1 displacement device 100. FIG. 2 shows a number of parameters which are used in the description that follows. More particularly, W_(C) is the width of single coil trace 126. P_(C) is the coil trace pitch—i.e. the distance between two adjacent coil traces 126 of the same layer 128.

In some embodiments, each layer 128 of coil traces 126 is fabricated such that: the coil trace pitch P_(C)=λ/N, where N is a positive integer and λ is the above-discussed spatial magnetic wavelength of magnet arrays 112; and W_(C) is set close to P_(C) such that there is a minimum acceptable gap (P_(C)−W_(C)) between adjacent coil traces 126. For example, the trace gap P_(C)−W_(C) can be set at 50˜100 μm (e.g. less than 200 μm). It will be appreciated that the minimum possible acceptable trace gap will depend on a number of factors, including, without limitation, the amount of current expected to be carried in each coil trace, the capability of the PCB fabrication process and the heat dissipating characteristics of the system 100. FIGS. 3A-3C schematically depict a number of possible embodiments of coil trace layers 128 which are fabricated to have these characteristics. In each of the FIG. 3A-3C embodiments, P_(C)=λ/6 (i.e. N=6) and W_(C) is set very close to P_(C) such that there is a minimum acceptable gap (e.g. less than 200 μm) between adjacent coil traces 126.

In some embodiments, each layer 128 of coil traces 126 is fabricated such that every MN/2 (where M is another positive integer number) adjacent coil traces 126 form one coil group 134, where coil traces 126 in the same group 134 can be either driven by separate amplifiers or be connected in a star pattern and driven by a multi-phase amplifier. FIGS. 3A-3C show a number of different grouping arrangements that exhibit these characteristics. In FIG. 3A, M=2 and N=6, so each group 134 includes 6 adjacent coil traces 126. In some embodiments, each FIG. 3A group 134 may be driven by a corresponding three-phase amplifier (not shown). For example, the coil traces 126 labeled A1,B1,C1,A1′B1′,C1′ belong to one group 134. The symbol ′ used in FIG. 3A indicates reversing current. For example, the electrical current in trace A1′ is the same as that of trace A1 but in opposite direction. In FIG. 3B, M=1 and N=6, so each group 134 includes 3 adjacent coil traces 126. In some embodiments, each FIG. 3B group 134 may be driven by a corresponding three-phase amplifier (not shown). In FIG. 3C, M=3 and N=6, so each group 134 includes 9 adjacent coil traces 126. In some embodiments, each FIG. 3C group 134 may be driven by a corresponding three-phase amplifier (not shown). Like FIG. 3A, the symbol ′ used in FIG. 3C indicates reversing current. It will be appreciated in light of the foregoing that in general, every 3 n (n is a positive integer) adjacent coil traces 126 can form one group 134 driven by a corresponding three-phase amplifier.

In some embodiments, each layer 128 of coil traces 126 is fabricated such that the coil-trace width W_(C)=λ/5 and the coil trace pitch P_(C)=λ/k, where k is any number less than 5 and λ is the spatial magnetic period of magnet arrays 112. Setting W_(C)=λ/5 has the advantage that such a coil trace width minimizes the effect of fifth order magnetic fields generated by magnet arrays 112, because of a spatial filtering/averaging effect. FIGS. 3D-3E schematically depict a number of possible embodiments of coil trace layers 128 which are fabricated to have these characteristics. In each of the FIG. 3D-3E embodiments, W_(C)=λ/5 and the coil trace pitch P_(C)=λ/k.

In FIG. 3D, W_(C)=λ/5 and P_(C)=λ/k=λ/3. It can be seen from FIG. 3D, that adjacent coil traces 126 are relatively widely spaced apart from one another compared to those of the embodiments shown in FIGS. 3A-3C. In the FIG. 3D embodiment, every 3 adjacent coil traces 126 are grouped together to provide groups 134, wherein each group 134 may be driven by a corresponding three-phase amplifier (not shown). In general, coil traces 126 may be grouped such that every 3 n (n is a positive integer) adjacent coil traces 126 can form one group 134 which may be driven by one corresponding three-phase amplifier. FIG. 3E shows a layout where W_(C)=λ/5 and

$P_{C} = {\frac{\lambda}{k} = {\frac{\lambda}{4}.}}$

In the FIG. 3E embodiment, every 4 adjacent coil traces 126 are grouped together to provide groups 134. Groups 134 of the FIG. 3E embodiment may be driven by a corresponding two-phase amplifier. As before, the symbol ′ used to label coil traces 126 indicates reversing current. In general, coil traces 126 may be grouped such that every 2 n (n is a positive integer) adjacent coil traces 126 can form one group 134.

FIG. 3F shows a layout which combines the characteristics of the layouts of FIGS. 3A-3C and of FIGS. 3D-3E. More particularly, in FIG. 3F, the coil trace pitch P_(C)=λ/5 and W_(C) is set close to P_(C) such that there is a minimum acceptable gap between adjacent coil traces. It will be appreciated that these characteristics are similar to those of the embodiments of FIGS. 3A-3C. However, with W_(C) is set close to P_(C), W_(C) will be almost equal to W_(C)=λ/5 which is the characteristic of the embodiment of FIGS. 3D-3E. Accordingly, the layout in FIG. 3F can be used to minimize the effect of fifth order magnetic fields generated by magnet arrays 112 (as discussed above). In the FIG. 3F embodiment, every 5 adjacent coil traces 126 are grouped together to provide groups 134. Groups 134 of the FIG. 3F embodiment may be driven by a corresponding five-phase amplifier. In general, coil traces 126 may be grouped such that every 5 n (n is a positive integer) adjacent coil traces 126 can form one group 134 which may be driven by one corresponding five-phase amplifier.

FIG. 4A is a schematic partial cross-sectional view of multiple layers 128 (128A-128F) of coil traces 126 which may be used in stator 120 of the FIG. 1 displacement device 100. It can be seen from FIG. 4A, that layers 128A, 128C, 128E comprise Y-oriented coil traces 126Y and that layers 128B, 128D, 128F comprise X-oriented coil traces 126X. It can also be observed from FIG. 4A that Y-oriented coil traces 126Y in different layers 128A, 128C, 128E are aligned with one another in the X-direction—i.e. coil traces 126Y in layer 128A are aligned (in the X-direction) with coil traces 126Y in layers 128C, 128E. Although it can't be directly observed from the illustrated view of FIG. 4A, it can be appreciated that X-oriented coil traces 126X may exhibit a similar characteristic—i.e. coil traces 126X in layer 128B are aligned (in the Y-direction) with coil traces 126X in layers 128D, 128F. Coil traces 126X, 126Y in the same column (i.e. traces 126X aligned with one another in the Y-direction and/or traces 126Y aligned with other another in the X-direction) can be connected in serially, in parallel or independently of one another. It will be appreciated that the number of layers 128 can be any suitable number and is not limited to the six shown in FIG. 4A.

FIG. 4B is a schematic partial cross-sectional view of multiple layers 128 (128A, 128C, 128E, 128G) of coil traces 126 which may be used in stator 120 of the FIG. 1 displacement device 100. For clarity, only layers 128A, 128C, 128E, 128G having Y-oriented traces 126Y are shown in FIG. 4B—i.e. layers 128 having X-oriented coil traces 126X are not shown in FIG. 4B. It can also be observed from FIG. 4B that Y-oriented coil traces 126Y in different layers 128A, 128C, 128E, 128G are offset from one another in the X-direction—i.e. coil traces 126Y in layer 128A are offset from the next adjacent Y-oriented coil traces 126Y in layer 128C, coil traces 126Y in layer 128C are offset from the next adjacent Y-oriented coil traces 126Y in layer 128E and so on. In the illustrated embodiment, coil traces 126Y in layers 128A, 128E are aligned with one another in the X-direction and coil traces 126Y in layers 128C, 128G are aligned with one another in the X-direction—i.e. coil traces 126Y in every 2^(nd) layer 128 of Y-oriented coil traces 126Y are aligned with one another in the X-direction.

Although it can't be directly observed from the illustrated view of FIG. 4B, it can be appreciated that X-oriented coil traces 126X may exhibit similar characteristics—i.e. coil traces 126X in adjacent layers 128B, 128D, 128F, 128H of X-oriented coil traces 126X may be offset from one another in the Y-direction. In some embodiments, coil traces 126X in every 2^(nd) layer 128 of X-oriented coil traces 126X are may be aligned with one another in the Y-direction. Regardless of their offset, this description may refer to coil traces in the same “column”—for example, coil traces 126Y labeled a1, a2, a3, a4 may be referred to as being in the same column and coil traces 126Y labeled d1, d2, d3, d4 may be referred to as being in the same column Coil traces 126X, 126Y in the same column can be connected in serially, in parallel or independently of one another.

The amount of offset between adjacent layers 128 of Y-oriented coil traces 126Y is referred to as O_(L) and can be used to minimize the effect of higher order harmonics in the magnetic fields of magnet arrays 112. In some embodiments, O_(L) is designed at

${{\pm \frac{\lambda}{10}} + \frac{K\; \lambda}{5}},$

where K is a positive integer number. When O_(L) has this characteristic and adjacent Y-oriented traces in a particular column (for example, coil traces 126Y labeled a1 and a2) are driven with equal current, then the forces between the 5^(th) order harmonic magnetic field generated by a magnet array 112 and two offset traces 126Y in the same column (for example, coil traces a1 and a2) will tend to cancel one another out (i.e. attenuate one another). In some embodiments, O_(L) is designed at

${{\pm \frac{\lambda}{18}} + \frac{K\; \lambda}{9}},$

where K is a positive integer number. When O_(L) has this characteristic and adjacent Y-oriented traces 126Y in a particular column (for example, coil traces 126Y labeled a1 and a2) are driven with equal current, then the forces between the 9^(th) harmonic magnetic field generated by a magnet array 112 and two offset traces 126Y in the same column (for example, coil traces a1 and a2) will cancel one another out (i.e. attenuate one another).

In some embodiments, O_(L) can be designed in such a way that several harmonic fields are optimally attenuated to minimize overall force ripple effects caused by higher order harmonics of the magnetic field generated by magnet array 112. In some embodiments, O_(L) is designed at

$\pm \frac{\lambda}{2}$

and Y-oriented coils trace of adjacent Y-trace layers (e.g. coil traces 126Y labeled a1 and a2) are driven with opposite current. As a result, current flowing into one layer 128 can flow back from an adjacent layer 128 to form winding turns.

Driving Y-oriented traces 126Y in a particular column (for example coil traces a1 and a2) with equal currents is practical, because these coil traces 126Y may be serially connected, but may not be desirable to achieve ideal cancellation of 5^(th) order harmonics effects because the coil trace a1 is closer to the magnet array than the coil trace a2. In some embodiments, the effects of higher order magnetic field harmonics of magnet arrays 112 can be further reduced by providing O_(L) as discussed above and by driving Y-oriented traces 126Y in a particular column but in different layers 128 (for example, coil traces 126Y labeled a1 and a2) with different amounts of current. Assuming that coil trace layer 128A is closer to moveable stage 110 than coil trace 128C and so on, it will be appreciated that the magnetic field experienced by coil traces 126Y labeled a1 and a2 will not be identical. Accordingly, further attenuation of the effect of 5^(th) order harmonics of the magnetic field of magnet array 112 may be achieved by setting the current in the traces 126Y of layer 128C to be at least approximately e^(2π×5×G) ^(L) ^(/λ) times higher than the corresponding current in the traces 126Y of corresponding columns of layer 128A, where G_(L) is the center-to-center Z-direction spacing between Y-oriented coil traces 126Y in adjacent layers 128. For example, the current in coil trace 126Y labeled a2 can be set to be at least approximately a factor of e^(2π×5×G) ^(L) ^(/λ) times higher than the corresponding current in trace 126Y labeled a1. The current in the traces 126Y of a single column of every 2^(nd) layer 128 of Y-oriented coil traces 126Y (e.g. the current in traces 126Y labeled a1 and a3) may be set to be the same.

Similarly, some attenuation of the effect of 9^(th) order harmonics of the magnetic field of magnet array 112 may be achieved by setting the current in the traces 126Y of layer 128C to be at least approximately e^(2π×9×G) ^(L) ^(/λ) times higher than the corresponding current in the traces 126Y of corresponding columns of layer 128A, where G_(L) is the center-to-center Z-direction spacing between Y-oriented coil traces 126Y in adjacent layers 128. For example, the current in coil trace 126Y labeled a2 can be set to be at least approximately e^(2π×9×G) ^(L) ^(/λ) times higher than the corresponding current in trace 126Y labeled a1. The current in the traces 126Y of a single column of every 2^(nd) layer 128 of Y-oriented coil traces 126Y (e.g. the current in traces 126Y labeled a1 and a3) may be set to be the same.

It will be appreciated that similar offsets and/or similar current driving characteristics can be used for X-oriented coils 126X to reduce the effects of higher order magnetic fields associated with magnet arrays 112.

FIG. 5 is a schematic partial view of a single layer 128 of coil traces 126 showing a group connection scheme which may be used in displacement device 100 of FIG. 1. Layer 128 shown in FIG. 5 comprises a plurality of Y-oriented coil traces 126Y which are grouped into groups 134. As discussed above, coil traces 126Y in a group 134 may be driven by a common multi-phase amplifier. In the FIG. 5 embodiment, there are N_(G)=8 different groups 134 of coil traces 126Y (labeled Group 1-Group 8 in FIG. 5). Each group 134 of coil traces 126Y extends in the Y-direction and the groups 134 are laid out side-by-side along the X direction in a repeating pattern. In general, the number N_(G) of groups 134 of coil traces 126Y may be any suitable positive integer. To reduce the number of amplifiers (not shown) used to implement displacement device 100, coil traces 126Y belonging to particular groups 134 may be in serial connection. For example, all of the groups 134 of coil traces 126Y labeled Group 1 in FIG. 5 may be serially connected. When two or more coil traces 126Y in one layer are serially connected, the direction of current flow in such coil traces 126Y may be the same or opposite to one another. Within each group 134, each phase can either be driven by an independent amplifier, such as a H-bridge, or all phases are connected in a star pattern and driven by a multi-phase amplifier. In a special case, each of the FIG. 5 groups 134 includes only a single coil trace 126Y. At the cost of operational complexity and additional hardware, this special case embodiment permits maximum flexibility with respect to control of current location and, in turn, control of the movement of moveable stage 110. In this special case, groups 134 with the same group label (e.g. Group 1) can be serially connected and the direction of current flow in these traces 126Y can be the same or opposite to one another. It will be appreciated that similar group connection schemes may be used for X-oriented coils 126X in other layers 128.

It will be appreciated that even with the group connection implementation of FIG. 5, Y-oriented coil traces 126 in the same column but in different layers 128 (e.g. coil traces 126Y labeled a1, a2, a3, a4 in FIG. 4B) can also be connected serially and share a common amplifier. Similarly, it will be appreciated that even with the group connection implementation of FIG. 5, X-oriented coil traces 126 in the same column but in different layers can also be connected serially and share a common amplifier.

Since each phase of coil traces 126 has capacitance and there is mutual-capacitance among difference phases of coil traces 126, one or more external inductor(s) (not shown) can be serially inserted between an amplifier output terminal and a terminal of coil trace(s) 126. Such serial inductors can be installed on the planar coil PCB boards, and/or on amplifier circuit boards, and/or in the ends of the cables connecting amplifiers to planar coil assemblies. Adding such serial inductors may increase the inductance of the coil load and may thereby reduce the power loss of switching electronics of power amplifiers and reduce the current ripples in coil traces 126.

Magnet Array

FIGS. 6A and 6B (collectively, FIG. 6) are schematic partial cross-sectional views of layouts of magnet arrays 112 which may be used in moveable stage 110 of the FIG. 1 displacement device 100 and which are useful for showing a number of magnet array parameters. It can be observed that the layout of magnet arrays 112A, 112B, 112C, 112D in FIG. 6A is the same as that of magnet arrays 112A, 112B, 112C, 112D in FIG. 1B. The layout of magnet arrays 112A, 112B, 112C, 112D in FIG. 6B is similar to that of magnet arrays 112A, 112B, 112C, 112D shown in FIGS. 6A and 1B. The discussion in this section applies to both of the layouts shown in FIGS. 6A and 6B.

FIG. 6 shows that each magnet array 112 has a width of W_(m) and a length of L_(m). The spacing between two magnet arrays with the same elongation direction (i.e. between X-magnet arrays 112A, 112C or between Y-magnet arrays 112B, 112D) is denoted as spacing S_(m). It can be observed that in the illustrated embodiment, moveable stage 110 comprises a non-magnetic region 113 located in a center of its magnet arrays 112 and that the dimensions of non-magnetic region 113 are S_(m)−W_(m) by S_(m)−W_(m). As discussed above, for each magnet array 112, the magnetization segments 114 and corresponding magnetization directions are uniform along the dimension L_(m) and are oriented orthogonally to the dimension L_(m). For each magnet array 112, the magnetization segments 114 and corresponding magnetization direction vary along the direction of dimension W_(m). While not expressly shown in the illustrated views, the magnet arrays 112 shown in FIG. 6 may be mounted under a suitable table or the like which may be used to support an article (e.g. a semiconductor wafer) thereatop.

One implementation of magnet arrays 112 is described above in connection with FIG. 1D (for Y-magnet array 112B) and 1E (for X-magnet array 112A). In the description of magnet arrays that follows, a comprehensive explanation is provided in the context of an exemplary Y-magnet array 112B. X-magnet arrays may comprise similar characteristics where the X and Y directions and dimensions are appropriately interchanged. For brevity, in the description of Y-magnet array 112B that follows, the alphabetic notation is dropped and Y-magnet array 112B is referred to as magnet array 112. Similarly, the magnetization segments 114B of Y-magnet array 112B are referred to as magnetization segments 114.

FIG. 7A shows an embodiment of a magnet array 112 substantially similar to magnet array 112B described above in connection with FIG. 1D. Magnet array 112 is divided, along the X-axis, into a number of magnetization segments 114 which are generally linearly elongated in the Y-axis direction. In the illustrated embodiment, the magnetization directions of magnetization segments 114 have a spatial periodicity with a period (or wavelength) λ along the X-axis; the width W_(m) of magnet array 112 in the X-direction is given by W_(m)=N_(m)λ. where N_(m) is a positive integer (and N_(m)=2 in the FIG. 7A embodiment); the magnetization directions of the various magnetization segments 114 are oriented in directions orthogonal to the Y-axis; the X-axis widths of the various magnetization segments 114 are either: λ/(2 N_(t)) for the two outermost (edge) segments 114 or λ/N_(t) for the interior segments 114, where N_(t) represents the number of different magnetization directions in magnet array 112 (and N_(t)=4 in the FIG. 7A embodiment); and the magnetization of magnetization segments 114 is mirror symmetric about central Y-Z plane 118. It will be appreciated that with W_(m)=N_(m)λ and the magnetization of magnetization segments 114 being mirror symmetric about central Y-Z plane 118, the outermost (edge) segments 114 have X-axis widths that are half the X-axis widths of interior segments 114 and that the outermost edge segments 114 have magnetizations that are oriented in along the Z-direction.

FIG. 7B is another embodiment of a magnet array 112 suitable for use with the FIG. 1 displacement device. The FIG. 7B magnet array 112 has characteristics similar to those of the FIG. 7A magnet array 112, except that N_(m)=1 and N_(t)=4. It can be observed from FIG. 7B that the spatial magnetic period λ is defined even where the total X-axis width W_(m) of the magnet array is less than or equal to λ. In the FIG. 7B case, the magnetization directions of magnetization segments 114 of magnet array 112 may be considered to be spatially periodic in the X-direction with a period λ, even though there is only a single period.

As discussed above, magnet arrays 112 that exhibit the properties of those shown in FIGS. 7A and 7B eliminate or reduce cross-coupling forces from coil traces 126 oriented in X directions. Such characteristics of magnet arrays 112 shown in FIGS. 7A and 7B include: magnet arrays 112 including magnetization segments 114 which are generally elongated in the Y-direction with corresponding magnetizations oriented orthogonally to the Y-direction; the X-dimension width W_(m) of magnet arrays 112 is W_(m)=N_(m)λ where N_(m) is an integer and λ is the magnetic period λ described above; and magnet arrays 112 are mirror symmetric about a Y-Z axis that runs though the center of the X-dimension of magnet arrays 112.

FIGS. 7C and 7D show other embodiments of magnet arrays 112 suitable for use with the FIG. 1 displacement device. In these embodiments, the magnetization directions of magnetization segments 114 have a spatial periodicity with a period (or wavelength) λ along the X-axis; the width W_(m) of magnet array 112 in the X-direction is given by W_(m)=(N_(m)+0.5)λ where N_(m) is a non-negative integer (and N_(m)=0 in the FIG. 7C embodiment and N_(m)=1 in the FIG. 7D embodiment); the magnetization directions of the various magnetization segments 114 are oriented in directions orthogonal to the Y-axis; the magnetization of magnetization segments 114 is mirror anti-symmetric about central Y-Z plane 118; and the outermost (edge) segments 114 have magnetizations that are oriented in the Z-direction and X-axis widths of λ/(2 N_(t))=λ/8 (where N_(t)=4 in the embodiments of both FIGS. 7C and 7D) which are half of the X-axis widths λ/N_(t)=λ/4 for the interior segments 114. In the FIG. 7C case, the magnetization directions of magnetization segments 114 of magnet array 112 may be considered to be spatially periodic in the X-direction with a period λ, even though magnet array 112 exhibits less than a single period λ.

When the width W_(m) of magnet array 112 is a non-integer number of magnetic wavelengths λ (as in the case in the embodiments of FIGS. 7C and 7D, for example), then there will be coupling of force or moment to magnet array 112 from current flow in non-aligned coil traces 126 that interact with the magnetic field of array 112. For example, in the case of the Y-magnet arrays 112 shown in FIGS. 7C and 7D (which are mirror anti-symmetric about Y-Z plane 118), there will be coupling of moment in the rotational direction about Z to Y-magnet arrays 112 from current flow in coil traces oriented along the X-direction. This net moment can be compensated using suitable control techniques or using suitable arrangements of additional magnetic arrays 112 with different (e.g. opposite) magnetization patterns.

FIGS. 7E-7H show other embodiments of magnet arrays 112 suitable for use with the FIG. 1 displacement device. In these embodiments, the magnetization directions of magnetization segments 114 have a spatial periodicity with a period (or wavelength) λ along the X-axis; the width W_(m) of magnet array 112 in the X-direction is given by W_(m)=N_(m)λ/2, where N_(m) is a positive integer (and λ_(m)=1 in the FIG. 7E embodiment, N_(m)=2 in the FIG. 7F embodiment, N_(m)=3 in the FIG. 7G embodiment and N_(m)=4 in the FIG. 7H embodiment); the magnetization directions of the various magnetization segments 114 are oriented in directions orthogonal to the Y-axis; and the outermost (edge) segments 114 have magnetizations that are oriented along the X-axis and X-axis widths of λ/(2 N_(t))=λ/8 (where N_(t)=4 in the embodiments of FIGS. 7E and 7H) which are half of the X-axis widths λ/N_(t)=λ/4 for the interior segments 114. Note that the central Y-Z plane 118 is not explicitly shown in FIGS. 7E-7H. However, it will be appreciated that this Y-Z plane 118 divides the X-dimension of magnet array 112 in half.

In FIGS. 7E and 7G, the magnetization of magnetization segments 114 is mirror symmetric about central Y-Z plane 118, and the width W_(m) of magnet array 112 in the X-direction is not an integer number of spatial periods λ. In the case of Y-magnet arrays 112 shown in FIGS. 7E and 7G, there will be coupling of forces in the Y direction to Y-magnet arrays 112 from current flow in coil traces 126 oriented along the X-direction. This net force can be compensated for using suitable control techniques or using suitable arrangements of additional magnetic arrays 112 with different (e.g. opposite) magnetization patterns.

In FIGS. 7F and 7H, the magnetization of magnetization segments 114 is mirror anti-symmetric about central Y-Z plane 118, and the width W_(m) of magnet array 112 in the X-direction is an integer number of spatial periods A. In the case of Y-magnet arrays 112 shown in FIGS. 7F and 7H, there will be coupling of moment in the rotational direction around Z to Y-magnet arrays 112 from current flow in coil traces 126 oriented along the X-direction. This net moment can be compensated using suitable control techniques or using suitable arrangements of additional magnetic arrays 112 with different (e.g. opposite) magnetization patterns.

FIGS. 7I-7L show other embodiments of magnet arrays 112 suitable for use with the FIG. 1 displacement device. In these embodiments, the magnetization directions of magnetization segments 114 have a spatial periodicity with a period (or wavelength) λ along the X-axis; the width W_(m) of magnet array 112 in the X-direction is given by W_(m)=N_(m)λ/2, where N_(m) is a positive integer (and N_(m)=1 in the FIG. 7I embodiment, N_(m)=2 in the FIG. 7J embodiment, N_(m)=3 in the FIG. 7K embodiment and N_(m)=4 in the FIG. 7L embodiment); the magnetization directions of the various magnetization segments 114 are oriented in directions orthogonal to the Y-axis; and the X-axis widths of all of the magnetization segments 114 are λ/N_(t) (where N_(t)=4 in the illustrated embodiments of FIGS. 7I-7L. As the magnetization of magnetization segments in FIG. 7I-7L is not mirror symmetric about central Y-Z plane 118, there will be coupling of moment in the rotational direction around Z to Y-magnet arrays 112 from current flow in coil traces oriented along the X-direction. In addition, for the cases in FIGS. 7I and 7K, as the width W_(m) of magnet array 112 in the X-direction is not an integer number of spatial periods λ, there will be coupling of forces in the Y direction to Y-magnet arrays 112 from current flow in coil traces 126 oriented along the X-direction. This net force and moment can be compensated using suitable control techniques or using suitable arrangements of additional magnetic arrays 112 with different (e.g. opposite) magnetization patterns.

In some embodiments, magnet arrays 112 of FIGS. 7A-7L may be fabricated from unit magnetization segments 114 having Y-dimension lengths L_(m) and X-dimension widths λ/(2 N_(t)) or λ/(N_(t)) where Nt is the number of magnetization directions in a period λ as discussed above. In some embodiments, magnetization segments 114 having X-dimension widths λ/(N_(t)) may be fabricated from a pair of side-by-side magnetization segments 114 having X-dimensions widths λ/(2 N_(t)) and having their magnetization directions oriented in the same direction. In some embodiments, the Z-dimension heights of the unit magnetization segments 114 may be same as their X-dimension widths—e.g. λ/(2 N_(t)) or λ/(N_(t)).

As discussed above, a central non-magnetic spacer may be provided in magnet arrays 112. In embodiments which are symmetric or mirror symmetric about central Y-Z plane 118, such a non-magnetic spacer may divide the central magnetization segment 114 into a pair of “half-width” magnetization segments 114 (i.e. having X-dimensions widths similar to the X-dimension widths of the edge segments 114). The resultant magnet arrays 118 remain symmetric or mirror symmetric about a central Y-Z plane 118. In embodiments which are not symmetric about a central Y-Z plane 118, different patterns may be used.

FIGS. 8A-8L show magnet arrays 112 suitable for use with the FIG. 1 displacement device 100 in accordance with particular embodiments. The magnet arrays 112 of FIGS. 8A-8L have features similar to those of magnet arrays 112 of FIGS. 7A-7L, except that the magnet arrays 112 of FIGS. 8A-8L include non-magnetic spacers 136 centrally located (in their X-dimensions). Spacers 136 (of the Y-magnet arrays 112 shown in FIGS. 8A-8L) may be provided with a X-axis width g which is at least approximately equal to

${g = {\left( {\frac{N_{g}}{5} + \frac{1}{10}} \right)\lambda}},$

where N_(g) is a non-negative integer number. When the width g of spacers 136 exhibits this property, spacers 136 will have an attenuating (cancelling) effect on disturbance torques and/or forces created by the 5^(th) order harmonic field of magnet array 112. In general, the width g of the non-magnetic spacer 136 may be set to be at least approximately equal to

${= {\left( {\frac{N_{g}}{k} + \frac{1}{2k}} \right)\lambda}},$

where N_(g) has the above described properties and k is the order of the harmonic of the magnetic field to be attenuated. In some embodiments, spacers 136 (of the Y-magnet arrays 112 shown in FIGS. 8A-8L) may be provided with a X-axis width g which is at least approximately equal to

$g = {{\frac{K_{g}}{5}\lambda} - W_{c}}$

where K_(g) is a non-negative integer number and W_(c) is the X-axis width of coil traces 126 generally elongated in Y direction. When the width g of spacers 136 exhibits this property, spacers 136 will have an attenuating (cancelling) effect on disturbance torques and/or forces created by the 5^(th) order harmonic field of magnet array 112. In general, the width g of the non-magnetic spacer 136 may be set to be at least approximately equal to

${{\frac{K_{g}}{k}\lambda} - W_{c}},$

where K_(g) and W_(c) have the above described properties and k is the order of the harmonic of the magnetic field to be attenuated.

The magnet array 112 embodiments shown in FIGS. 8A and 8B have two sides arranged on either X-direction side of non-magnetic spacer 136. Both the left and right sides (in the illustrated view) of the FIG. 8A magnet array 112 have magnetization patterns similar to those of magnet array 112 of FIG. 7A; and both the left and right sides of the FIG. 8B magnet array 112 have magnetization patterns similar to those of magnet array 112 of FIG. 7B. The X-direction width W_(side) of each side of the magnet arrays 112 of FIGS. 8A and 8B (i.e. the X-direction distance between an edge of array 112 and the edge of non-magnetic spacer 136) is W_(side)=N_(m)λ where N_(m) is a positive integer and the total X-direction width of the magnet arrays 112 of FIGS. 8A and 8B is W_(m)=2 N_(m)λ+g, where N_(m)=2 in FIG. 8A and N_(m)=1 in FIG. 8B.

The magnet array 112 embodiments shown in FIGS. 8C and 8D have two sides arranged on either X-direction side of non-magnetic spacer 136. The left (in the illustrated view) sides of magnet arrays 112 shown in FIGS. 8C and 8D have magnetization patterns similar to those of magnet arrays 112 shown in FIGS. 7C and 7D respectively. The right (in the illustrated view) sides of magnet arrays 112 shown in FIGS. 8C and 8DF have magnetization patterns that are opposite those of the left sides—i.e. as if the left side of the magnet array 112 was duplicated in the location of the right side of the magnet array 112 and then each individual magnetization segment 114 in the right side of the magnet array 112 was rotated 180° about its own central axis along which it is linearly elongated. The X-direction width W_(side) of each side of the magnet arrays 112 of FIGS. 8C and 8D is W_(side)=(N_(m)−0.5)λ where N_(m) is a positive integer and the total X-direction width of the magnet arrays 112 of FIGS. 8C and 8D is W_(m)=(2 N_(m)−1)λ+g, where N_(m)=1 in FIG. 8C and N_(m)=2 in FIG. 8D.

Similarly, the magnet array 112 shown in FIGS. 8E, 8G, 8I, 8K have two sides arranged on either X-direction side of non-magnetic spacer 136, with their respective left (in the illustrated view) sides having magnetization patterns similar to FIGS. 7E, 7G, 7I, 7K magnet array 112 and their respective right (in the illustrated view) sides having magnetization patterns that are the opposite to those of the left (in the illustrated view0 sides, where “opposite” has the same meaning as discussed above for the case of FIGS. 8C and 8D. The X-direction widths W_(side) of each side of the magnet arrays 112 of FIGS. 8E, 8G, 8I, 8K is W_(side)=(N_(m)−0.5)λ where N_(m) is a positive integer and the total X-direction width of the magnet arrays 112 of FIGS. 8E, 8G, 8I, 8K is W_(m)=(2 N_(m)−1)λ+g, where N_(m)=1 in FIG. 8E, N_(m)=2 in FIG. 8G, N_(m)=1 in FIG. 8I, N_(m)=2 in FIG. 8K.

The magnet arrays 112 shown in FIGS. 8F, 8H, 8J, 8L have two sides arranged on either X-direction side of non-magnetic spacer 136, with both their left and right sides having magnetization patterns similar to those of magnet arrays 112 of FIGS. 7F, 7H, 7J, 7L, respectively. The X-direction width W_(side) of each side of the magnet arrays 112 of FIGS. 8F, 8H, 8J, 8L is W_(side)=N_(m)λ where N_(m) is a positive integer and the total X-direction width of the magnet arrays 112 of FIGS. 8F, 8H, 8J, 8L is W_(m)=2 N_(m)λ+g, where N_(m)=1 in FIG. 8F, N_(m)=2 in FIG. 8H, N_(m)=1 in FIG. 8J, N_(m)=2 in FIG. 8L. The magnet arrays 112 shown in FIGS. 8A-8L may be fabricated in a manner similar to that described above for FIGS. 7A-7L.

Layout of Magnet Arrays

As discussed above, FIGS. 6A and 6B show layouts of the magnet arrays 112 which may be used in moveable stage 110 of displacement device 100 in accordance with particular embodiments. In accordance with particular embodiments, when arranging magnet arrays 112 on moveable stage 110, the spacing S_(m) between two adjacent parallel arrays (e.g. between a pair of X-magnet arrays 112, such as X-magnet array 112A and X-magnet array 112C in the case of the FIG. 6 embodiment and/or between a pair of Y-magnet arrays 112, such as Y-magnet arrays 112B and Y-magnet arrays 112D, in the case of the FIG. 6 embodiment) may be selected to be at least approximately

${S_{m} = {\left( {N_{S} + \frac{1}{2}} \right)P_{C}}},$

where N_(S) is a non-negative integer number and P_(C) is the coil trace pitch discussed above (see FIG. 2). When a plurality of parallel magnet arrays 112 are designed with this spacing characteristic, this spacing characteristic will help to minimize or reduce force and/or torque ripples which may be generated by the discrete nature (i.e. finite dimensions) of coil traces 126.

In some embodiments, when arranging magnet arrays 112 on moveable stage 110, the spacing S_(m) between two adjacent parallel arrays (e.g. between a pair of X-magnet arrays 112, such as X-magnet array 112A and X-magnet array 112C in the case of the FIG. 6 embodiment and/or between a pair of Y-magnet arrays 112, such as Y-magnet arrays 112B and Y-magnet arrays 112D, in the case of the FIG. 6 embodiment) may be selected to be at least approximately S_(m)=(2 N_(S)+1)λ/12, where N_(S) is a non-negative integer number. When a plurality of parallel magnet arrays 112 are designed with this spacing characteristic, this spacing characteristic will help to minimize or reduce 6 cycle-per-λ, force and/or torque ripples which may be generated by the interaction between 5^(th) harmonics magnetic field of magnet arrays 112 and current flowing in coil traces 126.

In some embodiments, two adjacent parallel magnet arrays 112 (e.g. a pair of X-magnet arrays 112, such as X-magnet array 112A and X-magnet array 112C in the case of the FIG. 6 embodiment and/or a pair of Y-magnet arrays 112, such as Y-magnet arrays 112B and Y-magnet arrays 112D, in the case of the FIG. 6 embodiment) may comprise magnetization segments 114 with magnetization orientations that are the same as one another. This characteristic is shown, for example, in FIG. 9A where Y-magnet array 112B and Y-magnet array 112D comprise magnetization segments 114B, 114D with magnetization orientations that are the same as one another. In some embodiments, two adjacent parallel magnet arrays 112 may comprise magnetization segments 114 with magnetization orientations that are the opposites of one another—i.e. as if each magnetization segment 114 is individually rotated 180° about a corresponding central axis along which it is linearly elongated. This characteristic is shown, for example, in FIG. 9B, where magnet array 112B and magnet array 112D comprise magnetization segments 114B, 114D with magnetization orientations that are opposite to one another.

In some embodiments, the spacing S_(m) is designed to be at least approximately

${S_{m} = {N_{S}\frac{\lambda}{2}}},$

where N_(S) is a positive integer. Where the spacing of adjacent parallel magnet arrays 112 (e.g. a pair of X-magnet arrays 112, such as X-magnet array 112A and X-magnet array 112C in the case of the FIG. 6 embodiment and/or a pair of Y-magnet arrays 112, such as Y-magnet arrays 112B and Y-magnet arrays 112D, in the case of the FIG. 6 embodiment) are designed to have this feature, then the current distribution in the active coil traces 126 for each parallel magnet array 112 can be substantially similar in spatial distribution (i.e. in phase), provided that the parallel magnet arrays 112 have the same magnetization pattern and N_(S) is even or the parallel magnet arrays 112 have opposite magnetization patterns and N_(S) is odd.

As discussed above, the layout of magnet arrays 112 shown in FIGS. 6A and 6B provides for a non-magnetic region 113 located between magnet arrays 112. In some embodiments, the dimensions (S_(m)−W_(m)) of this non-magnetic region 113 may be designed to have the characteristics that (S_(m)−W_(m))≧λ, such that active coil traces 126 for two parallel magnet arrays 112 don't interfere with one another.

In some embodiments, the dimension L_(m) of magnet arrays 112 shown in FIGS. 6A and 6B is set at least approximately equal to L_(m)=N_(L)λ, where N_(L) is a positive integer number. Where magnet arrays 112 exhibit this characteristic, there will be a further reduction in the coupling force generated between a magnet array 112 and current flowing in coil traces 126 in directions orthogonal to the elongated dimension of magnet array 112.

The layout of magnet arrays 112 shown in FIGS. 6A and 6B is not the only possible layout for magnet arrays 112 that could be used for moveable stage 110 of the FIG. 1 displacement device 100. More particularly, a number of other possible layouts of magnet arrays 112 suitable for use in moveable stage 110 of the FIG. 1 displacement device 100 are shown in FIGS. 10A-10D.

FIG. 10A shows a schematic cross-sectional view of layout of magnet arrays 112A, 112B, 112C, 112D which may be used for moveable stage 110 of the FIG. 1 displacement device 100 in accordance with a particular embodiment. The FIG. 10A layout of magnet arrays 112 differs from the FIG. 6 layout of magnet arrays 112 because magnet arrays 112 are shaped (e.g. as squares) such that non-magnetic region 113 is eliminated and all of the undersurface area of moveable stage 110 is occupied by magnet arrays 112. In the illustrated embodiment of FIG. 10A, each magnet array 112 comprises a pattern of magnetization segments 114 having the characteristics as those shown in FIG. 7A, although it will be appreciated that magnet arrays 112 of the FIG. 10A layout could be provided with magnetization segments 114 exhibiting characteristics of any of the magnet arrays 112 described herein—e.g. exhibiting any of the magnetization patterns shown in FIGS. 7A-7L and 8A-8L.

FIG. 10B shows a schematic cross-sectional view of a layout of magnet arrays 112A-112P which may be used for moveable stage 110 of the FIG. 1 displacement device 100 in accordance with another embodiment. The layout of FIG. 10B differs from the layout of FIG. 10A in that the layout of FIG. 10B includes more than four magnet arrays 112. In the illustrated embodiment, magnet arrays 112A, 112C, 112E, 112G, 112I, 112K, 112M, 112O are X-magnet arrays and magnet arrays 112B, 112D, 112F, 112H, 112J, 112L, 112N, 112P are Y-magnet arrays. The FIG. 10B layout comprising more than four magnet arrays 112 may be used, for example, where moveable stage 110 is relatively large.

FIG. 10C shows a schematic cross-sectional view of a layout of magnet arrays 112 which may be used for moveable stage 110 of the FIG. 1 displacement device 100 according to another embodiment. For brevity, only Y-magnet arrays 112A1, 112A2, 112A3, 112B1, 112B2, 112B3, 112C1, 112C2, 112C3, 112D1, 112D2, 112D3 are expressly labeled in FIG. 10C, although it will be appreciated that X-magnet arrays are also shown in FIG. 10C. Magnet arrays 112 with the same orientation (e.g. X-magnet arrays or Y-magnet arrays) and aligned with one another in the direction orthogonal to the direction of elongation of their magnetization segments may be referred to herein as a set of aligned magnet arrays. For example, Y-magnet arrays 112A1, 112A2, 112A3 are a set of aligned Y-magnet arrays, because they have the same orientation (they are Y-magnet arrays elongated along the Y-axis) and are aligned with one another in a direction (the X-direction) orthogonal to the direction of elongation of their respective magnetization segments. A set of aligned magnet arrays may be driven by current flow in the same coil traces 126 of stator 120 (not shown in FIG. 10C). For example, the set of aligned Y-magnet arrays 112A1, 112A2, 112A3 may be driven by current flow in the same coil traces 126 of stator 120. Similarly, the set of aligned Y-magnet arrays 112B1, 112B2, 112B3 may be driven by the same coil traces 126 of stator 120, the set of aligned Y-magnet arrays 112C1, 112C2, 112C3 may be driven by the same coil traces 126 of stator 120 and the set of aligned Y-magnet arrays 112D1, 112D2, 112D3 may be driven by the same coil traces 126 of stator 120.

Because of the spacing between each set of aligned Y-magnet arrays (e.g. the set of aligned Y-magnet arrays 112A1, 112A2, 112A3) and the adjacent set(s) of aligned Y-magnet arrays (e.g. the adjacent set of aligned Y-magnet arrays 112B1, 112B2, 112B3), each set of aligned Y-magnet arrays can be driven independently by its corresponding active coil traces 126 without significant coupling from adjacent sets of aligned Y-magnet arrays. In the FIG. 10C embodiment, there is also an offset between the actuating force center of the set of aligned Y-magnet arrays 112A1, 112A2, 112BA3 and the set of aligned Y-magnet arrays 112B1, 112B2, 112B3, these two sets of aligned Y-magnet arrays can be used to generate two levitating forces (i.e. the Z-direction) and two lateral (i.e. in the X-direction) forces.

In the illustrated embodiment of FIG. 10C, there are four sets of aligned Y-magnet arrays: a first set of aligned Y-magnet arrays 112A1, 112A2, 112A3; a second set of aligned Y-magnet arrays 112B1, 112B2, 112B3; a third set of aligned Y-magnet arrays 112C1, 112C2, 112C3; and a fourth set of aligned Y-magnet arrays 112D1, 112D2, 112D3, and each set of aligned Y-magnet arrays can independently generate two forces (one levitation force (in the Z-direction) and one lateral force (in the X-direction)). Three or more sets of aligned Y-magnet arrays having a Y-direction offset (e.g. the offset of the actuating force center between the first set of aligned Y-magnet arrays 112A1, 112A2, 112A3 and the second set of aligned Y-magnet arrays 112B1, 112B2, 112B3) may alone be used to provide actuating forces and torques in 5 degrees of freedom—i.e. forces in the X and Z directions and moment around the X, Y and Z axes. The only actuating force that cannot be provided by three or more sets of aligned Y-magnet arrays having a Y-direction offset is force in the Y-direction in FIG. 10C.

In the illustrated embodiment of FIG. 10C, there are four sets of aligned Y-magnet arrays: a first set of aligned Y-magnet arrays 112A1, 112A2, 112A3; a second set of aligned Y-magnet arrays 112B1, 112B2, 112B3; a third set of aligned Y-magnet arrays 112C1, 112C2, 112C3; and a fourth set of aligned Y-magnet arrays 112D1, 112D2, 112D3. While not explicitly enumerated with reference numerals, those skilled in the art will appreciate that the illustrated embodiment of FIG. 10C also include four sets of aligned X-magnet arrays, each of which can independently generate two forces (one levitation force (in the Z-direction) and one lateral force (in the Y-direction)). With all of the sets of aligned arrays capable of being independently driven by their corresponding active coil traces 126, the FIG. 10C magnet array layout provides a significant amount of over actuation. These over-actuating capabilities can be used to control the flexible mode vibration of moveable stage 110, for moveable stage shape correction and/or for vibration suppression. It will be appreciated by those skilled in the art that the layout of FIG. 10C provides four sets of aligned X-magnet arrays and four sets of aligned Y-magnet arrays, but some embodiments may comprise larger numbers or smaller numbers of sets of aligned X and Y-magnet arrays. Also, it will be appreciated by those skilled in the art that the layout of FIG. 10C provides that each set of aligned X-magnet arrays and each set of aligned Y-magnet arrays comprises three individual magnet arrays, but some embodiments may comprise different numbers of individual magnet arrays in each set of aligned magnet arrays.

FIG. 10D shows a schematic cross-sectional view of a layout of magnet arrays 112 which may be used for moveable stage 110 of the FIG. 1 displacement device 100 according to another embodiment. FIG. 10D also schematically depicts the coil traces 126 that may be used to actuate the various sets of aligned X and Y-magnet arrays 112. It should be noted that the coil traces 126 shown in FIG. 10D are schematic in nature and do not represent the dimensions or numbers of coil traces 126. The layout of magnet arrays 112 in FIG. 10D is similar to that of FIG. 10C, except that in FIG. 10D each set of aligned X and Y-magnet arrays 112 comprises a pair of individual magnet arrays 112 (instead of three individual magnet arrays, as is the case in FIG. 10C). More particularly, the layout of FIG. 10D comprise four sets of aligned X-magnet arrays with two individual magnet arrays in each set and four sets of aligned Y-magnet arrays with two individual magnet arrays in each set. The sets of X-magnet arrays in the FIG. 10D layout include: a first set of aligned arrays 112 a 1, 112 a 2; a second set of aligned arrays 112 b 1, 112 b 2; a third set of aligned arrays 112 c 1, 112 c 2; and a fourth set of aligned arrays 112 d 1, 112 d 2. The sets of Y-magnet arrays in the FIG. 10D layout include: a first set of aligned arrays 112A1, 112A2; a second set of aligned arrays 112B1, 112B2; a third set of aligned arrays 112C1, 112C2; and a fourth set of aligned arrays 112D1, 112D2.

As is the case for the layout of FIG. 10C, sets of aligned magnet arrays in the FIG. 10D layout may be driven by the same set of coil traces 126 on stator 120. More particularly: the first set of aligned X-magnet arrays 112 a 1, 112 a 2 may be driven by coil traces 126 a 1/a2; the second set of aligned X-magnet arrays 112 b 1, 112 b 2 may be driven by coil traces 126 b 1/b2; the third set of aligned X-magnet arrays 112 c 1, 112 c 2 may be driven by coil traces 126 c 1/c2; and the fourth set of aligned X-magnet arrays 112 d 1, 112 d 2 may be driven by coil traces 126 d 1/d2. Similarly: the first set of aligned Y-magnet arrays 112A1, 112A2 may be driven by coil traces 126A1/A2; the second set of aligned Y-magnet arrays 112B1, 112B2 may be driven by coil traces 126B1/B2; the third set of aligned Y-magnet arrays 112C1, 112C2 may be driven by coil traces 126C1/C2; and the fourth set of aligned Y-magnet arrays 112D1, 112D2 may be driven by coil traces 126D1/D2. It will be appreciated that the active coil traces for each set of aligned magnet arrays are not static but are determined dynamically based on the current position of moveable stage 110 and the desired movement of moveable stage 110.

As is the case with FIG. 10C discussed above, the layout of FIG. 10D includes a significant amount of over actuation. These over-actuating capabilities can be used to control the flexible modes of moveable stage 110, for moveable stage shape correction and/or for moveable stage vibration suppression. It will be appreciated by those skilled in the art that the layout of FIG. 10D provides four sets of aligned X-magnet arrays and four sets of aligned Y-magnet arrays, but some embodiments may comprise larger numbers or smaller numbers of sets of aligned X and Y-magnet arrays. Also, it will be appreciated by those skilled in the art that the layout of FIG. 10D provides that each set of aligned X-magnet arrays and each set of aligned Y-magnet arrays comprises a pair of individual magnet arrays, but some embodiments may comprise different numbers of individual magnet arrays in each set of aligned magnet arrays.

The characteristics of each individual magnet array 112 in the layouts of FIGS. 10A-10D (e.g. the orientations of magnetization segments 114, the lengths L_(m), the widths W_(m) and the like) can be similar to any of those described herein—e.g. exhibiting any of the magnetization patterns shown in FIGS. 7A-7L and 8A-8L. The spacing S_(m) of adjacent arrays in FIGS. 10C, 10D can be similar to that described above for FIGS. 6A, 6B.

Field Folding and Current Commutation

In some embodiments, magnet arrays 112 comprise characteristics similar to so-called “Halbach arrays”. Usually, the magnetic field of a Halbach array is assumed to be primarily sinusoidal with a small amount of 5^(th) order harmonic distortion. This assumption is relatively accurate at locations well inside (i.e. away from the edges) of a long, multi-period Halbach array. However, at the edges of the Halbach array, the magnetic field is far from sinusoidal, particularly when the magnet array is only 1-2 magnetic periods (λ) wide as is the case, for example, in some of the magnet arrays 112 shown in FIGS. 7 and 8. The distortion of the magnetic field at the edges of magnet arrays 112 may be referred to as fringing field effects. Designing a commutation law to achieve at least approximately linear force characteristics for such a non-sinusoidal field can be difficult.

One technique to minimize the fringing field effects when using current carrying coil traces to impart forces on a Halbach array involves increasing the number of magnetic periods (λ) in the Halbach array. Although disturbance forces attributable to the fringing field are unchanged with the increased number of magnetic periods, the effect of such disturbance forces on the total amount of force imparted on the larger Halbach array is reduced. Another technique to minimize the fringing field effects when using current carrying coil traces to impart forces on a Halbach array involves only exciting coil traces that are located away from the edges of the Halbach array and the fringing fields. This second technique sacrifices force generation capacity.

The inventors have determined that it can be theoretically proven (using spatial convolution theory) that the forces (both lateral and vertical) between a magnet array of width W_(m) and an infinitely wide current array of period W_(m) are of identical magnitudes to the forces between an infinitely wide magnet array with period W_(m) and a single coil trace. This principle is illustrated in FIGS. 11A-11C. FIG. 11A shows a short Y-magnet array 112 of width W_(m) moving laterally (i.e. in the X-direction in the illustrated view) relative to a single coil trace 126 excited with constant current. This FIG. 11A arrangement produces non-sinusoidal forces due to the interaction of coil trace 126 with the fringing fields at or near the edge of magnet array 112. In FIG. 11B, extra coil traces 126′ excited with the same amount of current as original coil trace 126 are added to form an infinitely wide current array of period W_(m). The resulting total force between magnet array 112 and the array of coil traces 126, 126′ becomes sinusoidal with a small component caused by the 5^(th) order harmonic. In FIG. 11C, forces are generated between the current in a single coil trace 126 and an infinitely wide periodic magnet array 112 of period W_(m).

The total forces between magnet array 112 and the arrays of coil traces 126, 126′ in the arrangement of FIG. 11B are the same as the forces between magnet array 112 and single coil trace 126 in the arrangement of FIG. 11C, if all coil traces 126, 126′ are excited with the same amount of current. This same principal applies to any of the magnet arrays 112 shown in FIGS. 7 and 8. In practical terms, the FIG. 11B infinite coil array is not required and it is sufficient to excite extra coil traces up to about λ/2 or greater beyond the edges of magnet array 112. This equivalence significantly simplifies the force analysis. Using this principle and standard three phase sinusoidal commutation, the actuating force on magnet array 112 (and a moveable stage 110 comprising a plurality of magnet arrays 112) has excellent linear characteristics, which is desirable for high speed precision applications.

FIG. 11D is a schematic cross-sectional view showing one layer 128 of coil traces 126 and a single magnet array 112 that may be used in the FIG. 1 displacement device 100 and how the field folding principle of FIGS. 11A-11C may be used in practice. Active (current carrying) coil traces 126 are shown as solid black; traces 126 shown in white represent either inactive coil traces 126 or active coil traces 126 for other magnet arrays (not shown). In the illustrate view of FIG. 11D, magnet array 112 is a Y-magnet array having magnetization segments 114 which are generally linearly elongated in the Y-direction. As can be seen from FIG. 11D, coil traces 126 are excited below magnet array 112 and out to a field folding length L_(FF) beyond each X-axis edges of magnet array 112. Coil traces 126 beyond this zone (i.e. greater than L_(FF) away from the X-axis edges of magnet array 112) can be either inactive, or be activated for other magnet arrays or may also be activated for the illustrated magnet array 112. Depending on the gaps between adjacent magnet arrays (e.g. the gap S_(m)−W_(m) shown in FIG. 6), L_(FF) can be set a suitable distance which balances the desirability of extending beyond the X-axis edges of magnet array 112 and avoiding force coupling with an adjacent magnet array. In some embodiments, L_(FF) can be set at L_(FF)=N_(ff)λ/2, where N_(ff) is a positive integer. In some embodiments, L_(FF) can be set at anything greater than or equal to λ/2. With a field folding length of L_(FF) on either side of the edges of magnet array 112, the current direction and magnitude of commutating laws can be designed in the same way as done in the situation where magnet array 112 is infinitely extended on both sides. This means that all active coil traces 126 on the same layer 128 for the same magnet array 112 follow the same commutation law (most commonly sinusoidal commutation) except that coil traces 126 have electrical phase shifts relative to one another.

FIG. 12 is a schematic cross-sectional view showing one layer 128 of coil traces 126 and a single Y-magnet array 112 which are useful for describing the determination of current commutation. The FIG. 12 magnet array 112 is a Y-magnet array 112 meaning that its magnetization segments 114 are generally linearly elongated in the Y-direction. FIG. 12 shows one active coil trace 126 (shown in black), with all other coil traces 126 (whether active or inactive) shown in white. FIG. 12 includes a coordinate frame X_(m)-Y_(m)-Z_(m), fixed with magnet array 112, where the Z_(m) axis origin is at the bottom surface of magnet array 112, the X_(m) axis origin is in the center of magnet array 112. With these definitions, the magnet field in the space below the bottom surface of magnet array 112 can be modeled according to:

$\quad\left\{ \begin{matrix} {{B_{z}\left( {x_{m},z_{m}} \right)} = {B_{0}{\cos \left( \frac{x_{m}}{\lambda_{c}} \right)}^{z_{m}/\lambda_{c}}}} \\ {{B_{x}\left( {x_{m},z_{m}} \right)} = {{- B_{0}}{\cos \left( \frac{x_{m}}{\lambda_{c}} \right)}^{z_{m}/\lambda_{c}}}} \end{matrix} \right.$

where λ_(c)=λ/2π and (x_(m), z_(m)) is an arbitary point in the space below the bottom surface of magnet array 112. Although magnet array 112 is finite in its X-axis width, its magnetic field can be modelled as if magnet array 112 is infinitely extended in the X-direction with the periodic magnetization pattern of magnetization segments 114 continuously repeated. Due to the field folding method used, this modelling assumption does not significantly impact the accuracy of the force calculations. As shown in FIG. 12, a coil trace 126 is located (i.e. centered) at (x_(m), z_(m)). Regardless of whether the position (x_(m), z_(m)) of this coil trace 126 is right under magnet array 112 or beyond the X-dimension edges of magnet array 112, we can excite this coil trace 126 for this magnet array 112 according to:

${I = {{{- k}\; F_{ax}{\cos \left( \frac{x_{m}}{\lambda_{c}} \right)}^{- \frac{z_{m}}{\lambda_{c}}}} - {k\; F_{az}{\sin \left( \frac{x_{m}}{\lambda_{c}} \right)}^{- \frac{z_{m}}{\lambda_{c}}}}}},$

Where: I is a current in the trace 126 at the position (x_(m), z_(m)); F_(αx) and F_(αz) represent the desired forces imparted on magnet array 112 in X and Z directions, respectively; k is an actuator constant coefficient; and the current reference direction (positive current direction) is consistent with Y_(m) axis (i.e. if current flows into the page in FIG. 12 then I is positive). When all active current traces 126 for magnet array 112 are excited according to the above commutation law (of course, each trace 126 can have different current amplitude/direction, since each coil trace 126 has distinct spatial location), actuating forces imparted on magnet array 112 will be F_(αx) and F_(αz). Coil traces 126 in the same lateral location (e.g. in the same X-axis location in FIG. 12), but different layers 128 can be either serially connected (i.e. having the same current) or individually controlled. When they are serially connected, the desired current amplitude for coil traces 126 in the same lateral location but in different layers 128 can be calculated based on the location of the coil trace 126 on the uppermost layer 128.

As discussed above, some magnet arrays 112 (e.g. the magnet arrays shown in FIGS. 8A-8L) comprise non-magnetic spacers 136. For such magnet arrays 112, determination of coil trace current can be done by assuming that non-magnetic spacer 136 is not present and by assuming that each side of the magnet array 112 is moved toward its center (i.e. toward Y-Z plane 118) by half the width g of spacer 136. This process is shown schematically in FIGS. 13A and 13B, where current commutation is calculated for the actual FIG. 13A magnet array 112 on the basis of the assumption that the FIG. 13A magnet array 112 has the properties of the FIG. 13B magnet array 112. With these assumptions, the inventors have determined that the actual resulting forces will not be equal to the calculated values (F_(αx),F_(αz)), but will be scaled by a scaling factor (e.g. 95%) which may be fixed using suitable control algorithm(s) and/or the like. Such differences can be accommodated using suitable control techniques, such as setting the desired forces to be slightly larger than would be desired if spacer 136 was not present. As discussed above, spacer 136 has the benefit that it can reduce the effect of the 5^(th) order harmonic of the magnetic field of magnet array 112.

Sensor Systems

To accurately control the position of moveable stage 110 relative to stator 120 in displacement device 100 (e.g. to the precision desired for a typical lithography process and/or the like), it is desirable to know the relative positions of moveable stage 110 and stator 120. As discussed above, the forces imparted on moveable stage 110 depend on the relative spacing between coil traces 126 (on stator 120) and magnetic arrays 112 (on moveable stage 110). An issue which can give rise to difficulty for determining these relative positions is motion of stator 120 which can be generated by ground vibration, by reaction forces on stator 120 and/or the like. FIG. 14A schematically illustrates one embodiment of a sensing system 200 for separately measuring the positions of moveable stage 110 and stator 120 relative to a metrology frame 202. In the illustrated embodiment, stator 120 is supported by a stator frame 204 (which may be supported by the ground or by another vibration isolation system (not shown)) and moveable stage 110 is floating above stator 120 under the influence of actuating forces caused by the interaction of magnet arrays and current carrying coil traces as discussed above. Stator frame 204 can provide mechanical support and thermal cooling for the coil assembly of stator 120.

Metrology frame 202 is supported by one or more vibration isolation mechanisms 206, which may be passive or active vibration isolation mechanisms 206, such as springs, air cylinders, air bearings and/or the like. Vibration isolation mechanisms 206 isolate metrology frame 202 from ground isolation. Metrology frame 202 may also be fabricated from suitable materials (e.g. thermally and mechanically stable materials). In the illustrated embodiment, metrology frame 202 provides a stable position reference for independently measuring the positions of both moveable stage 110 and stator 120 relative to the stable metrology frame 202. In the FIG. 14A view, Xm1, Zm1, Zm2 represent a number of the coordinates of the position of moveable stage 110 with respect to metrology frame 202. Although three dimensions of the relative position are shown in the FIG. 14A view, it should be understood that there may actually be 6 or more axis measurements associated with the position of moveable stage 110 relative to metrology frame 202. Any suitable position sensing devices may be used to determine these measurements. Non-limiting examples of suitable position sensors include: laser displacement interferometers, two-dimensional optical encoders, laser triangulation sensors, capacitive displacement sensors and/or the like.

Xs1, Zs2, and Zs2 shown in FIG. 14A represent coordinates of the position of stator frame 204 with respect to metrology frame 202. Although three dimensions of the relative position are shown in the FIG. 14A view, it should be understood that there may actually be 6 or more axis measurements associated with the position of stator frame 204 relative to metrology frame 202. Because the position of stator frame 204 relative to metrology frame 202 has only a small amount of variation, many low-cost and short-stroke position sensing devices are sufficient for measuring the position of stator frame 204. Non-limiting examples of suitable positions sensors include: capacitive displacement sensors, eddy current displacement sensors, optical encoders, laser triangulation sensors and/or the like. It will be appreciated that while the position of stator frame 204 may not be exactly known due to manufacturing errors, thermal loading and/or the like, these factors cause DC or low-frequency uncertainties in measurement of the position of stator frame 204 relative to metrology frame 202 and may be overcome by controlling the position of moveable stage 110 using a control scheme having sufficiently high gain at low frequencies (e.g. an integrating control element by way of non-limiting example0 to effectively attenuate these uncertainties. That is, a control scheme can be designed such that the position of moveable stage 110 is adjusted at a rate much faster than the low frequency uncertainties associated with the measurement of the position of stator frame 204. AC or relatively high frequency components of the position of stator frame 204 are more important. It is therefore desirable to measure these high frequency components using position sensors of suitably high bandwidth.

FIG. 14B shows another embodiment of a sensor system 220 for measuring a position of moveable stage 110. In the illustrated embodiment, moveable stage 110 comprises: a plurality of magnet arrays 112, a moving stage structure 226 and one or more sensor targets 224. Conveniently, one or more sensor targets 224 may be located in the space 230 (see FIG. 1B) between magnet arrays 112. Stator frame 204 comprises one or more sensor read heads 222. These heads 222 may be installed inside holes in the coil assembly of stator 120. Sensor heads 222 may interact optically, electrically, electromagnetically and/or the like with sensor targets 224 to measure the relative position of moving stage 110 relative to stator frame 204. By way of non-limiting example: sensor targets 224 may comprise optical two-dimensional grating plates and sensor heads 222 may comprise optical encoder read heads; sensor targets 224 may comprise conductive plates with two dimensional grid features and sensor heads 222 can comprise capacitive displacement measurement probes; sensor targets 224 can comprise reflective surfaces suitable for interferometry and sensor heads 222 may comprise laser interferometry heads; and/or the like.

Different position sensing techniques can be combined to provide an overall system. It will be appreciated that sensor heads 222 could be located on moveable stage 110 and sensor targets 224 could be located on stator frame 204. Also, in the FIG. 14B embodiment, the position of moveable stage 110 is measured relative to stator frame 204. In some embodiments, the same types of sensor targets 224 and sensor heads 222 could be located on moveable stage 110 and on a metrology frame 202 to measure the position of moveable stage 110 relative to metrology frame 202 in a system similar to that of FIG. 14A. Still further, it will be appreciated that FIG. 14B only shows the measurement of one or several dimensions, but other dimensions may be measured using similar techniques.

FIG. 14C shows another embodiment of a sensor system 240 suitable for use with the FIG. 1 displacement device 100. Moveable stage 110 is provided with a plurality of identifiable markers 242 (such as light emitting diodes (LEDs), reflective marker surfaces and/or the like, for example). A stereo camera 244 can acquire images of these markers 242 and, from the image locations of these markers 242, a suitably programmed controller 246 can determine the spatial positions of these markers 242 relative to stereo camera 244. The FIG. 14C embodiment shows that multiple moveable stages (e.g. moveable stage 110 and second moveable stage 110A having markers 242A) can be sensed using the same camera 244 and controller 246. Accordingly, system 240 can measure the relative position between two moveable stages 120. It will be appreciated by those skilled in the art that suitable markers can also be located on stator frame 204 to obtain the positions of the moveable stages referenced to stator frame 204.

It will be appreciated that the above described sensor systems have their own advantages and disadvantages, such as cost, measurement range/volume, resolution, accuracy, incremental or absolute position, sensitivity to line-of-sight block. Two or more of the above described sensor systems can be combined to achieve desired performance characteristics.

Motion Control

FIG. 15 shows a schematic block diagram of a control system 300 suitable for use in controlling the FIG. 1 displacement device 100. Control system 300 may be implemented by a suitable programmed controller (not expressly shown). Such a controller (and components thereof) may comprise hardware, software, firmware or any combination thereof. For example, such a controller may be implemented on a programmed computer system comprising one or more processors, user input apparatus, displays and/or the like. Such a controller may be implemented as an embedded system with a suitable user interface comprising one or more processors, user input apparatus, displays and/or the like. Processors may comprise microprocessors, digital signal processors, graphics processors, field programmable gate arrays, and/or the like. Components of the controller may be combined or subdivided, and components of the controller may comprise sub-components shared with other components of the controller. Components of the controller, may be physically remote from one another. The controller is configured to control one or more amplifiers (not expressly shown) to drive current in coil traces 126 and to thereby controllably move moveable stage 110 relative to stator 120.

In the schematic diagram of FIG. 15, V_(r) represents the reference motion command signals which define the trajectory of moveable stage 110 desired by the application process. V_(r) is typically a vector, prescribing the desired trajectory for moveable stage 110 in a manner which comprises multiple degrees of freedom. Such multiple degrees of freedom may include states corresponding to rigid body motion and/or vibration mode motion. As V_(r) is defined by a specific application process and from the application process point of view, V_(r) is not necessarily in the form desired for defining the motion of the center of gravity of moveable stage 110 and/or the vibration mode coordinate format. For example, V_(r) may specify the motion of a point on a wafer surface in a photolithography application where the wafer is installed on top of moveable stage 110, instead of specifying the motion of the center of gravity of moveable stage 110. In such cases, V_(r) may be converted to a corresponding vector Φ_(r), defined in a modal coordinate frame of reference, via reference position coordinate transform block 302.

The vector Φ_(r) may comprise, for example:

$\Phi_{r} = \begin{bmatrix} q_{r\; 1} \\ q_{r\; 2} \\ q_{r\; 3} \\ q_{r\; 4} \\ q_{r\; 5} \\ q_{r\; 6} \\ q_{r\; 7} \\ q_{r\; 8} \end{bmatrix}$

where q_(r1), . . . q_(r6) represent desired (reference) motion values for 6 states which define rigid body motion (e.g. 3 translational states and 3 rotational states) and q_(r7), q_(r8) represent reference values for two flexible vibration mode states. It will be appreciated that some embodiments may use different numbers of rigid body states and/or flexible mode states.

In the schematic diagram of FIG. 15, V_(f) represents the outputs of position feedback sensors 305 which includes information relating to the measured position of moveable stage 110. Typically, V_(f) will also be converted into a motion vector Φ_(f) in the modal coordinate frame via a feedback position coordinate transform block 304. The vector Φ_(f) may comprise, for example:

$\Phi_{f} = \begin{bmatrix} q_{f\; 1} \\ q_{f\; 2} \\ q_{f\; 3} \\ q_{f\; 4} \\ q_{f\; 5} \\ q_{f\; 6} \\ q_{f\; 7} \\ q_{f\; 8} \end{bmatrix}$

where q_(f1), . . . q_(f6) represents feedback values (e.g. feedback position values) for the 6 states which define rigid body motion (e.g. 3 translational states and 3 rotational states) and q_(f7), q_(f8) represent feedback values for two flexible vibration mode states.

With Φ_(r) as inputs, a feedforward control force/torque vector F_(f) (modal domain force/torque) may be calculated by a feedforward motion controller 306. With Φ_(e)=Φ_(r)−Φ_(f) as inputs, a feedback control force/torque vector F_(b) (modal domain force/torque) may be calculated by a feedback motion controller 308. The total modal domain force/torque vector is calculated as F_(φ)=F_(f)+F_(b). An actuator force coordinate transform block 310 may be used to convert the modal domain force/torque vector F_(φ) into force commands F_(a) for each magnet array 112. For each magnet array, its corresponding active coil current vector I_(a) (including current values for each trace) can be calculated from F_(a) according to an active coil current commutation algorithm performed by block 312, as discussed above. According to the position Φ_(f) of moving stage 110, a current coordinate transform may be performed by block 314 to determine the coil trace reference current I_(sr) for each group of stator coil traces 126. For each group of coil traces 126, this reference current I_(sr) will be: zero (inactive); or the active coil current I_(a) for a particular magnet array 112; or the combination of the currents for active coils currents for a plurality of magnet arrays 112. The stator coil reference current commands I_(sr) may be provided to power amplifiers 316 to drive moveable stage 110, and the actual stator coil currents provided by amplifiers 316 is represented by I_(s).

All 6 (or even more) degrees-of-freedom of moveable stage 110 may be measured for optimum motion control of moveable stage 110. However, in certain situations, some of the sensors or part of a sensor may fail or become dysfunctional, or for cost-related reasons, there may be fewer sensors installed at certain space within the working volume of moveable stage 110. These are examples of circumstances in which not all 6 degrees of positional freedom of moveable stage 110 are measured and which may be referred to as under-sensing. Some embodiments provide a motion control method for control of moveable stage 110 in under-sensed circumstances. When the sensor system does not provide measurement in the Z-direction (i.e. the levitating direction), the Z-component of the desired force for each magnet array 112 may be set at a constant level, for example, the Z-component of the force on each magnet array 112 may be set to a fraction of the gravitational force on moveable stage 110. Further, the above-described commutation equation may be changed to:

${I = {{{- k}\; F_{ax}{\cos \left( \frac{x_{m}}{\lambda_{c}} \right)}^{- \frac{z_{0}}{\lambda_{c}}}} - {k\; F_{az}{\sin \left( \frac{x_{m}}{\lambda_{c}} \right)}^{- \frac{z_{0}}{\lambda_{c}}}}}},$

where a nominal constant vertical position z₀ is used for each magnet array 112 instead of the actual relative height of the magnet array 112 above the coil traces 126, where the nominal constant vertical position z_(o) is the nominal position of the coil traces 126 in the coordinate frame of the moveable stage. For example, in some embodiments, z_(o)=−1 mm. Due to the fact that the Z-direction (levitation) force increases when the height of the magnet array 112 above the coil traces 126 decreases, a constant value of z₀ will result in a passive levitating effect. This passive levitating effect may be relatively more susceptible to external forces than active control of the Z-direction of moveable stage 110, but this passive levitating effect can still ensure that moveable stage 110 is floating above stator 120 without mechanical contact. By way of non-limiting example, this passive Z-direction control strategy is useful when it is desired to move moveable stage 110 within a non-critical working zone, for lower cost applications, for application which are otherwise more tolerant to positional uncertainty and/or the like.

A special case under-sensed scenario may occur where sensed position measurement of moveable stage 110 is only available for the X and Y translational position and for the rotational degree of freedom around Z. In this case, the above-described passive control mechanism can ensure stability in the Z translation direction, rotation around the X axis and rotation around the Y axis.

Multiple Moveable Stages

In certain applications, such as photo-lithography, automated assembly systems and/or the like, there can be a desire to simultaneously and independently control more than one moveable stage. This may be achieved, for example, by providing a corresponding plurality of independently controllable stators and controlling the movement of one moveable stage on each stator. In some circumstances, it is desirable to interchange the moveable stages (e.g. to move a moveable stage from one stator to another stator).

FIGS. 16A-16D schematically depict a method 400 for interchanging moveable stages 110 between multiple stators 120 according to one embodiment of the invention. More particularly, method 400 involves the movement of moveable stage 110A from stator 120A to stator 120B and moveable stage 110B from stator 120B to stator 120A. Method 400 involves the use of at least one intermediate stator 120C. In FIG. 16A, moveable stages 110A and 110B are shown operating on their respective stators 120A, 120B. In FIG. 16B, moveable stage 110A is moved from stator 120A to intermediate stator 120C. In FIG. 16C, moveable stage 110B is moved from stator 120B to stator 120A. In FIG. 16D, moveable stage 110A is moved from intermediate stator 120C to stator 120B.

FIG. 17A schematically depicts a method 420 for interchanging moveable stages 110 between multiple stators 120 according to another embodiment of the invention. Stators 102A, 120B are independently controlled. In an initial stage of method 420, moveable stage 110A works on stator 120A and moveable stage 110B works on stator 120B, concurrently and independently. To swap stators, moveable stage 110A and moveable stage 110B can be caused to move in the arrows shown in FIG. 17A. This movement imparts momentum on moveable stages 110A, 110B. When the two moveable stages 110A, 110B (or more precisely their corresponding X-magnet arrays 112) overlap along the X-direction (i.e. when some X-oriented coil traces extend under X-magnet arrays 112 of both moveable stages 110A, 110B), then the “shared” X-oriented coil traces (or all of the X-oriented coil traces) can be turned off, while desired Y-oriented coil traces remain active. Due to the over-actuation discussed above, the system may still actively control the motion of moveable stages 110A, 110B with 5 degrees of freedom (with Y-direction translation being the only uncontrolled motion). Because of their Y-direction momentum, the two moveable stages 110A, 110B can smoothly pass one another without touching or bumping into each other. It should be noted that the meeting location of two stages 110A, 110B is not necessarily at the borders of two stators 120A, 120B. In general this meeting location can be anywhere on any stator 120A, 120B or between the two stators 120A, 120B.

FIG. 17B schematically depicts how two moveable stages 110A, 110B can be controlled with six degrees of freedom of motion for each moveable stage on one stator 120. In the FIG. 17B embodiment, the two moveable stages 110A, 110B (or, more precisely, their corresponding magnet arrays 112) have non-overlapping locations in the X-direction and partially overlapping locations in the Y-direction. Accordingly, with the illustrated configuration, the X-oriented coil traces for moveable stages 110A, 110B can be independently activated, but moveable stages 110A, 110B (or more precisely the magnet arrays 112 of moveable stages 110A, 110B) share a number of Y-oriented coil traces. However, with the configuration shown in FIG. 17B, there are also a number of Y-oriented coil traces that only extend under one or more magnet arrays 112 of moveable stage 110A and a number of Y-oriented coil traces that only extend under one or more magnet arrays 112 of moveable stage 110B. The “shared” Y-oriented coil traces can be de-activated, but with the active X-oriented coil traces and at least some independently controllable Y-oriented coil traces, moveable stages 110A, 110B can still be independently controlled with 6 degree-of-freedom. In the illustrated configuration of FIG. 17B, moveable stages 110A, 110B are shown immediately adjacent one another in the Y-direction. While this configuration is possible, it is not necessary and moveable stages 110A, 110B can be spaced apart in the Y-direction. Further, in FIG. 17B, moveable stages 110A, 110B (or more precisely their magnet arrays 112) are shown at partially overlapping locations in the Y-direction, but moveable stages 110A, 110B (or more precisely their magnet arrays 112) could also be independently controlled if they were spaced apart from one another in the X-direction (i.e. completely non-overlapping in the Y-direction). The moveable stages in FIG. 17B could be made to pass one another in the X-direction and/or the Y-direction using the technique described above in FIG. 17A—e.g. moveable stage 110A could be moved to the right (in the illustrated view) of moveable stage 110B or moveable stage 110A could be moved below (in the illustrated view) moveable stage 110B. It will be appreciated that an analogous situation could occur with the two moveable stages 110A, 110B (or more precisely their magnet arrays 112) have non-overlapping locations in the Y-direction and partially overlapping (or non-overlapping) locations in the X-direction.

In some applications, it may be desirable to move moveable stages 110 through a number of different stages. FIG. 18 schematically illustrates an apparatus 460 suitable for this purpose. In the illustrated embodiment, moveable stages 110A-110D move between several stators 120A-120F and, in some applications, may stop at each stator 120 for some operation. In general, there may be any suitable number of moveable stages 110 and any suitable number (greater than the number of moveable stages 110) of stators 120. On each stator 120A-120F, a motion control system of the type described herein may be used to control positions of the corresponding moveable stage 110A-110D. In some embodiments, precision position control may only be required inside stators 120A-120F. Consequently, stator-to-stator motion may be guided by relatively inexpensive positions measurement systems, such as indoor GPS, stereo camera and/or the like.

Rotary Displacement Device

There is industrial demand for rotary displacement devices which have some Z-direction motion (e.g. on the scale of millimeters) together with rotary motion about the Z-axis. FIG. 19A is a horizontal cross-sectional view of a rotary displacement device 500 according to an embodiment of the invention. FIGS. 19B and 19C respectively depict a bottom cross-sectional view of the moveable stage (rotor) 510 of displacement device 500 and a top view of the stator 520 of displacement device 500. As can be seen best from FIG. 19B, moveable stage 510 comprises a magnet array 512 having magnetization segments 514 which are elongated in radial directions and which have circumferentially oriented magnetization directions. As is the case with the XY moveable stages discussed above, the orientation of the magnetization directions of magnetization segments 514 are generally orthogonal to the directions in which they are longitudinally extended—i.e. in the case of rotary displacement device 500, the circumferential orientation of magnetization directions of magnetization segments 514 is generally orthogonal to the directions (radial) in which magnetization segments 514 are physically elongated.

In the illustrated embodiment, magnet array 512 has an angular spatial magnetization period λ. In some embodiments, the number of spatial magnetic periods λ, in magnet array 512 is a positive integer number N_(m). In the particular case of the illustrated embodiment, N_(m)=8, so the angle subtended by each spatial magnetic period is λ=360°/8=45°. In other embodiments, N_(m) can have a different value. In some embodiments, magnet array 512 may comprise a non-integer number of spatial magnetic periods λ. By way of non-limiting example, in some embodiments magnet array 512 could comprise (N_(m)+0.5)λ spatial magnetic periods. As is the case with the XY embodiments described herein, the width of each magnetization segment 514 is a function of the number N_(t) of magnetization directions in a full spatial magnetic period λ. In the case of the illustrated embodiment, N_(t)=4 and so the angular width of each magnetization segment 514 is λ/N_(t)=λ/4=11.25°. In some embodiments, N_(t) can have a different value.

FIG. 19C shows how stator 520 comprises plurality of radially oriented coil traces 526. It will be appreciated that current travelling radially in coil traces 526 is capable of imparting force on magnet array 112 in both circumferential directions (e.g. directions having X and/or Y components) and in the Z-direction. In the particular case of the illustrated embodiment, coil traces 526 are divided into a plurality (e.g. four) of groups (labeled Groups 1-4) and shown delineated by dashed lines. Because of the geometrical location of the groups of coil traces 526, coil traces 526 in Groups 1 and 3 impart Z-direction and primarily Y-direction forces on magnet array 512, while coil traces in Groups 2 and 4 impart Z-direction and primarily X-direction forces on magnet array 512. The Z-direction forces can be controlled to generate Z-direction translation as well as rotation about the X and Y axes. The X and Y-direction forces can be controlled to generate torques (and corresponding rotation) about the Z-axis and can also be controlled to generate X and Y translation (if desired). Accordingly, with suitable control of current in coil traces 526, moveable stage 510 of displacement device 500 can be precisely controlled as a rotary displacement device, but can also be controlled with all six degrees of freedom. It will be appreciated that the particular grouping of coil traces 526 shown in FIGS. 19A-C represents only one possible embodiment. As is the case with any of the XY embodiments described herein, each coil trace 526 may be individually controlled for maximum flexibility. Also, different grouping arrangements of coil traces 526 may also be provided. Coil traces 526 may be connected serially or in parallel to achieve various design objectives.

In the illustrated embodiment, stator 520 comprises a plurality (e.g. four) sensor heads 521 which interact with one or more corresponding sensor targets 519 on moveable stage 510 to measure or otherwise sense rotary orientation of moveable stage 510 about the Z-axis and X and Y translational positions of moveable stage 510. In one particular embodiment, sensor heads 521 comprise encoder read heads and sensor target 519 comprises an encoder disk. In the illustrated embodiment, stator 520 also comprises a plurality (e.g. four) capacitive sensors 523 which can be used to measure or otherwise detect the Z-direction height of moveable stage 510 relative to stator 520 and the rotational orientation of moveable stage 510 about the X and Y axes. It will be appreciated that the sensors shown in the particular embodiment of FIG. 19 represent only one particular embodiment of a suitable sensor system which may be used with a rotary displacement device, such as rotary displacement device 500 and that other sensing systems could be used.

FIG. 19D is a bottom cross-sectional view of a moveable stage (rotor) 510′ according to another embodiment which may be used with displacement device 500 (i.e. in the place of moveable stage 510. Moveable stage 510′ differs from moveable stage 510 in that moveable stage 510′ comprises a plurality of angularly spaced apart magnet arrays 512′. In the case of the illustrated embodiment, moveable stage 510′ comprises four magnet arrays 512′. Each magnet array 512′ has an angular spatial magnetization period λ. In some embodiments, the number of spatial magnetic periods λ in each magnet array 512′ is a positive integer number N_(m), such that the angle subtended by each array is W_(m)=N_(m)λ. In the particular case of the FIG. 19D embodiment, N_(m)=1. In some embodiments, N_(m) can have a different value. In some embodiments, the angle subtended by each array 512 is W_(m)=(N_(m)+0.5)λ where N_(m) is a non-negative integer. As is the case with the XY embodiments described herein, the width of each magnetization segment 514 is a function of the number N_(t) of magnetization directions in a full spatial magnetic period λ. In the case of the illustrated embodiment, N_(t)=4 and so the angular width of each magnetization segment 514 is λ/N_(t)=λ/4. In some embodiments, λ_(t) can have a different value. In some embodiments, magnet arrays 512 can comprise magnetization segments 514 having angular widths of λ/2 N_(t). As in the case of the XY embodiments described above, such “half-width” magnetization segments 514 having angular widths λ/2 N_(t) may be provided at the edges of magnet array 512, although this is not necessary and such half-width magnetization segments can be used at other locations.

FIG. 19E is a top view of a stator 520′ according to another embodiment which may be used with displacement device 500 (i.e. in the place of stator 520). Stator 520′ differs from stator 520 in that stator 520′ comprises a plurality of layers 528A, 528B (e.g. two in the case of the illustrated embodiment) of coil traces 526′ wherein the coil traces 526′ in adjacent layers 528A, 528B are spatially (angularly) offset from one another by an offset angle O_(L). In some embodiments, the offset angle O_(L) can be set at least approximately to

${{\pm \frac{\lambda}{10}} + \frac{K\; \lambda}{5}},$

where K is an integer number. When the offset angle O_(L) exhibits this property, this offset can tend to cancel force/torque ripples which may be caused by the fifth order harmonic magnetic fields of magnet arrays 512. It should be noted that both the moveable stage 510′ of FIG. 19D and the stator 520′ of FIG. 19E can be used at the same time.

Other Layouts and Configurations

FIG. 20A schematically depicts a displacement device 600 according to another embodiment. Displacement device 600 comprises a moveable stage (not explicitly shown) which comprises a plurality of magnet arrays 612. In the illustrated embodiment, displacement device 600 comprise three magnet arrays 612 (labeled 612A, 612B, 612C). Each magnet array 612A, 612B, 612C comprises a corresponding plurality of magnetization segments 614A, 614B, 614C which are generally linearly elongated at a particular orientation in the X-Y plane—for example, magnetization segments 614A of magnet array 612A have one orientation of linear elongation, magnetization segments 614B of magnet array 612B have a second orientation of linear elongation and magnetization segments 614C of magnet array 612C have a third orientation of linear elongation. As is the case with the other displacement devices described herein, the magnetization directions of magnetization segments 614A, 614B, 614C may be generally orthogonal to the direction that they are physically elongated. Other than for their relative orientations, the characteristics of magnet arrays 612 and magnetization segments 614 may be similar to those discussed above for magnet arrays 112 and magnetization segments 114.

Displacement device 600 also comprises a stator (not explicitly shown) that comprises a plurality of generally linearly elongated coil traces 626. In the illustrated embodiment, displacement device 600 comprise three sets of coil traces 626 (labeled 626A, 626B, 626C) which may be located on corresponding layers (not explicitly shown) of the stator. Each layer of coil traces 626A, 626B, 626C may comprise coil traces 626A, 626B, 626C that are generally linearly elongated at a particular orientation in a corresponding X-Y plane. Such layers and their corresponding coil traces 626A, 626B, 626C may overlap one another (in the Z-direction) in the working region of displacement device 600. Other than for their relative orientations, the characteristics of coil traces 626 may be similar to those of coil traces 126 discussed above.

Displacement device 600′ shown in FIG. 20B is similar to displacement device 600, except that the orientations of the linearly elongated coil traces 626A′, 626B′, 626C′ are different than the orientations of the linearly elongated traces 626A, 626B, 626C and the orientations at which magnetization segments 614A′, 614B′ and 614C′ extend are different than the orientations at which magnetization segments 614A, 614B, 614C extend.

FIG. 20C schematically depicts a displacement device 700 according to another embodiment. Displacement device 700 comprises a moveable stage (not explicitly shown) which comprises a plurality of magnet arrays 712. In the illustrated embodiment, displacement device 700 comprises two magnet arrays 712 (labeled 712A, 712B). Each magnet array 712A, 712B comprises a corresponding plurality of magnetization segments 714A, 714B which are generally linearly elongated at a particular orientation in the X-Y plane—for example, magnetization segments 714A of magnet array 712A have one orientation of linear elongation and magnetization segments 714B of magnet array 712B have a second orientation of linear elongation. As is the case with the other displacement devices described herein, the magnetization directions of magnetization segments 714A, 714B may be generally orthogonal to the direction that they are physically elongated. Other than for their relative orientations, the characteristics of magnet arrays 712 and magnetization segments 714 may be similar to those discussed above for magnet arrays 112 and magnetization segments 114.

Displacement device 700 also comprises a stator (not explicitly shown) that comprises a plurality of generally linearly elongated coil traces 726. In the illustrated embodiment, displacement device 700 comprise two sets of coil traces 726 (labeled 726A, 726B) which may be located on corresponding layers (not explicitly shown) of the stator. Each layer of coil traces 726A, 726B may comprise coil traces 726A, 726B that are generally linearly elongated at a particular orientation in a corresponding X-Y plane. Such layers and their corresponding coil traces 726A, 726B may overlap one another (in the Z-direction) in the working region of displacement device 700. Other than for their relative orientations, the characteristics of coil traces 726 may be similar to those of coil traces 126 discussed above.

It will be appreciated that displacement device 700 of the FIG. 20C embodiment will not be able to provide all six degrees of freedom. With suitable control techniques, the embodiment of FIG. 200 C may be capable of providing motion with 4 degrees of freedom.

FIGS. 20A-20C are useful to demonstrate a feature of one aspect and particular embodiments of the invention. Some of the herein-described embodiments include relatively large numbers of magnet arrays. While this can achieve over-actuation which may enhance the ability to control the movement of the moveable stage relative to the stator, this is not necessary. Particular embodiments may comprise moveable stages having any suitable plurality (as few as two) magnet arrays, wherein each such magnet array comprises a plurality of magnetization sections that are generally linearly elongated along a corresponding direction, provided that the directions of linear elongation of all of the magnet arrays span the X-Y plane of the moveable stage. While the preferred directions of linear elongation may comprise at least two orthogonal directions (which may make control calculations relatively more simple), this is not necessary. In the case where the magnet arrays are aligned in a single moveable stage XY plane, any two or more non-parallel directions of linear elongation will span the XY plane. In currently preferred embodiments where six degrees of freedom are desired, three of more magnet arrays are provided with at least two of the magnet arrays being linearly elongated in non-parallel directions and with the force-centers of the three magnet arrays being non-co-linear. In addition, the directions of magnetization of the magnetization segments in each magnet array are generally orthogonal to the direction in which the magnetization segments are linearly elongated. Within a magnet array, the magnetization of the magnetization segments may have characteristics similar to any of those described herein—see FIGS. 7 and 8 for example.

Similarly, particular embodiments may comprise stators having coil traces elongated in any suitable plurality of directions, provided that the directions of linear elongation of the coil traces span a notional X-Y plane of the stator. While the preferred directions of linear elongation may comprise at least two orthogonal directions (which may make control calculations relatively more simple), this is not necessary. Any two or more non-parallel directions of linear elongation will span the notional XY plane of the stator. The XY plane of the stator may be referred to as a notional XY plane, since coil traces having different directions of linear elongation may be provided on different layers as discussed above. Such layers may have different locations in the Z-direction. Accordingly, the notional XY plane of the stator may be thought of as though the coil traces in each such layer were notionally brought to a single XY plane having a corresponding single location along the Z-axis.

The description set out above describes that there may be different numbers N_(t) of magnetization directions within a magnetic spatial period λ. However, N_(t)=4 for all of the illustrated embodiments described above. FIGS. 21A-21C schematically depict magnet arrays 802A, 802B, 802C having different values of N_(t)—i.e. different numbers of magnetization directions within a particular magnetic period λ. Magnet array 802A of FIG. 21A has N_(t)=4, magnet array 802B of FIG. 21B has N_(t)=2 and magnet array 802C of FIG. 21C has magnet array N_(t)=8. The number N_(t) may be selected to be any suitable number, with the advantage of having relatively large N_(t) is that relatively large N_(t) provides the corresponding magnet array with a relatively large fundamental harmonic and relatively small higher order harmonics at the expense of possibly greater cost and complexity in fabricating the magnet array.

As discussed above, the coil layouts shown in FIGS. 3D-3F (where W_(c)=λ/5) have an advantage that they may result in cancellation or attenuation of some of the effects of the 5^(th) order harmonic of the magnetic field created by a magnet array 112. FIG. 22A schematically shows a coil trace layout according to another embodiment which may be used in displacement device 100. Coil traces 126 in the FIG. 22A embodiment are skewed in the XY plane of moveable stage 110 by an amount O_(c) over the trace length L_(m). In some embodiments, the amount of skew O_(c) (which may be understood to be the X-direction distance traversed by Y-oriented trace 126 over its Y-dimension length L_(m)) may be selected to be λ/5 or λ/9 or λ/13 so as to result in attenuation of the 5^(th), or 9^(th) or 13^(th) order harmonic of the magnetic field created by a magnet array 112. This skew amount O_(c) may be adjusted to attenuate other harmonics by setting O_(c)=λ/n, where n is the number of the harmonic for which attenuation is desired. In the FIG. 22A embodiment, the x-dimension width W_(m) of coil trace 126 is shown as being λ/6, but this is not necessary in general and the Y-dimension width W_(m) may have other values. By way of non-limiting example, other than for the skew mentioned above, the layout of the FIG. 22A coil trace similar to any of the layouts shown in FIGS. 3A-3F).

It will be appreciated that Y-oriented coil traces 126 that are skewed in the manner shown in FIG. 22A will result in some possibly undesirable coupling between the Y-oriented coils and the X-magnet arrays 112. That is, current flowing in Y-oriented coil traces having the skew shown in FIG. 22A may impart forces or torques on X-magnet arrays 112. In the case of Y-oriented coil traces 126, such cross-coupling may be reduced or minimized by skewing the Y-oriented coil traces 126 in alternating layers 128 of Y-oriented traces 126 in opposing directions to have a canceling or attenuating effect on this cross coupling. FIG. 22B schematically illustrates a pair of adjacent layers 128 of Y-oriented coil traces 126. For clarity, the X-oriented coils between the layers 128 of Y-oriented coils 126 are not expressly shown. The Y-oriented coil traces 126 in adjacent layers 128 of the FIG. 22B embodiment are skewed in opposite directions in the X-Y plane. This opposing skew of the coil traces 126 in adjacent layers 128 may be used to reduce or minimize undesirable coupling between Y-oriented coils 126 and X-magnet arrays 112, while simultaneously reducing the effect of the 5th order harmonic of the magnetic field of the magnet arrays 112. As in the various embodiments of coil traces 126 described above, coil traces 126 in different layers 128 may be electrically connected in series, in parallel and/or individually.

FIGS. 23A-23D show various embodiments of Y-oriented coil traces 126 which (while generally linearly elongated in the Y-direction) exhibit a spatial triangle-wave which extends in the X-direction over a total X-direction peak-to-peak amplitude O_(c) and Y-direction spatial period τ_(c). In the illustrated embodiment, Y-direction spatial period τ_(c) is set to an integer factor of the Y-direction length L_(m) (e.g. L_(m) in FIG. 23A, L_(m)/2 in FIG. 23B, L_(m)/3 in FIG. 23C and L_(m)/4 in FIG. 23D) and the amplitude O_(c) is set to λ/5. These two characteristics of Y-oriented coil trace 126 can reduce the effect of the cross-coupling of Y-oriented trace with X-magnet arrays 112 and can also help to attenuate the effects of the 5th order harmonic of the magnetic field of arrays 112 on a single layer 128 of coil traces. It will be appreciated that setting the value of O_(c) to have different values can be used to cancel other harmonics (e.g. the 9^(th) order harmonic or the 13^(th) order harmonic) by setting O_(c)=λ/n, where n is the number of the harmonic for which attenuation is desired. Y-oriented coil traces 126 on adjacent Y-oriented layers 128 may be fabricated to have opposing triangular wave phase (e.g. opposing in the X-direction). FIGS. 23E and 23F show similar spatially periodic square wave and sinusoidal waveforms for Y-oriented coil traces 126, wherein the Y-direction spatial period τ_(c) is set to an integer factor of the Y-direction length L_(m) and the peak to peak amplitude O_(c) is set to λ/5 to attenuate the effect of the 5th order harmonic of magnet arrays 112.

FIG. 24C schematically depicts a Y-oriented coil trace 126 which results from the superposition of the square wave coil trace 126 of FIG. 24A and the triangular wave coil trace 126 of FIG. 24B. The FIG. 24A square wave has a spatial period τ_(c1) and an amplitude O_(c1) and the FIG. 24B triangular wave has a spatial period τ_(c2) and an amplitude O_(c2). Preferably, the spatial periods τ_(c1) and τ_(c2) are both set to an integer factor of the Y-direction length L_(m) of the coil 126. The amplitudes O_(c1) and O_(c2) may be set to different levels to attenuate the effects of more than one harmonic order of the magnetic field of magnet arrays 112. In general, the value of O_(c1) and O_(c2) may be set to different levels of O_(c1)=λ/n and O_(c2)=λ/m, where n and m are the numbers of the harmonics for which attenuation is desired.

In addition to or in the alternative to varying the linear elongation of coils 126 in effort to attenuate the effects of higher order harmonics of the magnetic fields of magnet arrays 112, some embodiments, may involve varying the linear elongation of magnet arrays 112 and their magnetization segments 114. FIG. 25A shows a magnet array 112 according to another embodiment which may be used in displacement device 100. Magnet array 112 shown in the illustrated embodiment of FIG. 25A is a Y-magnet array and its Y-dimension L_(m) is divided into a plurality of sub-arrays 112A, 112B, 112C, each of which is offset in the X-direction by a distance O_(m) from its adjacent sub-array. In the illustrated embodiment, sub-arrays 112A, 112C at the extremities of magnet array 112 have Y-dimensions of L_(m)/4 and sub-array 112B in the middle of magnet array 112 has a Y-dimension of L_(m)/2. In the illustrated embodiment, sub-arrays 112A, 112C are aligned with one another in the X-direction and are both offset in the X-direction from sub-array 112B by a distance O_(m). In some embodiments, it may be possible that sub-array 112C is offset from sub-array 112B in the same X-direction as sub-array 112B is offset from sub-array 112A.

In some embodiments, the offset O_(m) may be set at least approximately equal to

${O_{m} = {\left( {\frac{N_{m}}{5} - \frac{1}{10}} \right)\lambda}},$

where N_(m) is any integer number. Setting O_(m) to have this characteristic will tend to attenuate or cancel the effects of the interaction of the 5^(th) order harmonic of the magnet field of magnet array 112 with coil traces 126 that carry current in the Y-direction, thereby reducing or minimizing associated force ripples. In some embodiments, the offset O_(m) may be set at least approximately equal to O_(m) is set at

${\left( {\frac{N_{m}}{9} - \frac{1}{18}} \right)\lambda},$

to attenuate the effects of the interaction of the 9^(th) order harmonic of the magnetic field of magnet array 112 with coil traces 126 that carry current in the Y-direction. In some embodiments, the offset O_(m) may be set at least approximately equal to

${O_{m} = {{\frac{N_{m}}{5}\lambda} - W_{c}}},$

where N_(m) is any integer number and W_(c) is the X-axis width of coil traces 126 generally elongated in Y direction. Setting O_(m) to have this characteristic will tend to attenuate or cancel the effects of the interaction of the 5^(th) order harmonic of the magnet field of magnet array 112 with coil traces 126 that carry current in the Y-direction, thereby reducing or minimizing associated force ripples. In some embodiments, the offset O_(m) may be set at least approximately equal to O_(m) is set at

${{\frac{N_{m}}{9}\lambda} - W_{c}},$

to attenuate the effects of the interaction of the 9^(th) order harmonic of the magnetic field of magnet array 112 with coil traces 126 that carry current in the Y-direction.

In some embodiments, magnet arrays 112 may be provided with different numbers of sub-arrays. FIG. 25B shows a particular embodiment where the Y-dimension L_(m) of Y-magnet array 112 comprises a pair of sub-arrays 112A, 112B, each having a Y-dimension of L_(m)/2 and offset from one another by a distance O_(m) in the X-direction. The offset distance O_(m) of the FIG. 25B sub-arrays 112A, 112B can have the same characteristics as the offset distance O_(m) of the FIG. 25A sub-arrays. While magnet array 112 shown in the illustrated embodiment of FIG. 25A comprises three sub-arrays and magnet array 112 shown in the illustrated embodiment of FIG. 25B comprises two sub-arrays, magnet arrays 112 may generally be provided with any suitable number of sub-arrays having characteristics similar to those shown in FIGS. 25A and 25B.

FIGS. 25C and 25D show a number of embodiments of magnet arrays 112 which may be used to attenuate the effects of multiple spatial harmonics of their corresponding magnetic fields. FIGS. 25C and 25D show one embodiment of a Y-magnet array 112, which comprises six sub-arrays having Y-direction lengths

$\frac{L_{m}}{8}$

(labeled a,b,c,t,g,h in FIG. 25D) and one sub-array having Y-direction length

$\frac{L_{m}}{4}$

(labeled d-e in FIG. 25D), where L_(m) is the total Y-direction length of magnet array 112. FIG. 25D shows how some of sub-arrays (a, b, c, d-e, f, g, h) are shifted or offset (in the X-direction) relative to one another. In the embodiment of FIGS. 25C and 25D, sub-arrays b and g are aligned in the X-direction, sub-arrays a and h are shifted (rightwardly in the illustrated view) relatively to sub-arrays b and g by an amount O_(m2), sub-arrays d and e (together sub-array d-e) are shifted (rightwardly in the illustrated view) relatively to sub-arrays b and g by an amount O_(m1) and sub-arrays c and f are shifted (rightwardly in the illustrated view) relatively to sub-arrays b and g by an amount 2 O_(m2)+O_(m1). Each sub-array a,b,c,d-e,f,g,h of the illustrated embodiment has a X-dimension width W_(m). Mirror symmetry on line A-A (at the center of the Y-dimension L_(m) of magnet array 112) reduces or minimizes moment and/or force disturbance on the FIG. 25C, 25D magnet array 112. The harmonics attenuated by the FIG. 25C, 25D arrangement have spatial wavelengths equal to 2 O_(m1) and 2 O_(m2). For example, by setting O_(m1)=λ/10 and O_(m2)=λ/26, the 5^(th) and 13^(th) harmonics of the magnetic field are attenuated. In general, by setting O_(m1)=λ(M−0.5)/p, O_(m1)=λ(N−0.5)/q will greatly minimize disturbance moment/force resulting from harmonic magnetic fields of wavelength (spatial period) both λ/p and λ/q, where M and N are arbitrary integer numbers.

The techniques illustrated in FIGS. 25C-25D can be extrapolated so that field-induced disturbance moment and/or force effects associated with any suitable number of harmonics may be simultaneously attenuated using a suitable variation of these techniques. It is also possible to attenuate the field-induced effects of one harmonic order, but retain some level of net moment disturbance (such as shown in FIG. 25B).

Like the skewed coil traces 126 of FIGS. 22A, 22B and the spatially periodic coil traces 126 of FIGS. 23A-23F and 24C, magnet arrays 112 of particular embodiments can be skewed or provided with spatial periodicity along the direction that their respective magnetization segments 114 are generally linearly elongated. Such skewing and/or spatial periodicity of magnet arrays 112 may be used to reduce or minimize the effects of higher order harmonics of the magnetic fields of these magnet arrays 112. FIG. 26A shows a Y-magnet array 112 which is generally linearly elongated in the Y-direction, but which is skewed by an amount O_(p) in the X-direction over its Y-dimension length L_(m). Assuming that the FIG. 26A magnet array 112 is configured to interact with coil traces 126 having a rectangular geometry with a coil width W_(c) as defined above, then the skew amount may be set to be at least approximately equal to a non-negative value O_(p)=kΛ_(f)−W_(c), where Λ_(f) is the wavelength of the spatial harmonic of the magnetic field that is to be attenuated and k is a positive integer number. For example, if it desired to attenuate the effects of the 5^(th) order harmonic filed of the FIG. 26A magnet array 112, then O_(p) can be set to be kλ/5−W_(c) where k is a positive integer number.

FIGS. 26B and 26C show spatially periodic Y-magnet arrays 112, wherein an edge of each array 112 varies in the X-direction by an amount O_(p) over it Y-dimension length L_(m). The magnet arrays 112 of FIGS. 26B and 26C are periodic with a spatial period τ_(m) where τ_(m)=L_(m) in the FIG. 26B array and τ_(m)=L_(m)/2 in the FIG. 26C array. Like the case of the spatially periodic coil traces discussed above, the spatial period τ_(m) may generally be set to be an integer factor of the Y-dimension length L_(m). Also, similar to the case of the spatially periodic coil traces discussed above, spatially periodic magnet arrays may be provided with spatially periodic waveforms other than triangular waveforms, such as square waves, sinusoidal waveforms or superposed waveforms. The peak-to-peak amplitude parameter O_(p) can have the characteristics of the term O_(p) discussed above in connection with FIG. 26A.

In some embodiments, a combination of skewed coil traces and slanted magnet arrays may also be usefully implemented to eliminate internal stresses in the magnetic arrays while reducing or minimizing the effects of the interaction of current carrying coil traces with higher order harmonics of the magnetic fields of the magnet arrays.

While a number of exemplary aspects and embodiments are discussed herein, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. For example:

-   -   The coil traces shown in the embodiment of FIGS. 22, 23 and 24         are Y-oriented coil traces. It will be appreciated that         X-oriented coil traces could be provided with similar         characteristics. Similarly, the magnet arrays shown in the         embodiments of FIGS. 25 and 26 are Y-magnet arrays, but it will         be appreciated that X-magnet arrays could be provided with         similar characteristics. Also, the magnet arrays shown in the         embodiments of FIGS. 25 and 26 have a particular pattern of         magnetization. In general, these magnet arrays may be provided         with any suitable magnetization pattern, such as any of those         shown in FIGS. 7 and 8, for example.     -   For the purpose of minimizing or reducing eddy currents induced         by the motion of magnet arrays 112 on moveable stage 110, coil         traces 126 may be made relatively narrow. In some embodiments,         each coil trace 126 may comprise a plurality of sub-traces 126′.         Such an embodiment is shown schematically in FIG. 27A (in top         view) and in 27B (in cross-section). In coil traces 126A, 126B,         126C of FIG. 27A, each coil trace 126A, 126B, 126C comprises a         plurality of corresponding sub-traces 126A′, 126B′, 126C′         (collectively, sub-traces 126′) where each sub-trace 126′ has a         width T_(c) that is a fraction of the width W_(c) of its         corresponding coil 126. Each sub-trace 126′ only carries a         portion of the current flowing through its corresponding trace         126. Each sub-trace 126′ in the FIG. 27A embodiment is insulated         from its adjacent sub-trace 126′ by an insulator of width T_(f),         although it is not generally necessary for the insulator width         T_(f) to be uniform within a coil trace 126 and there is a         desire to minimize Tf, to achieve high surface fill factor. In         general, any suitable number of sub-traces 126′ may be provided         in each trace 126 depending on the trace width W_(c), the         sub-trace width T_(c) and the insulation with T_(f). The         sub-traces 126′ of each corresponding coil trace 126 may be         electrically connected in parallel at their ends (e.g. at their         Y-dimension ends in the case of the illustrated embodiment). The         regions where sub-traces 126′ are connected to one another may         be outside of the working region of device 100—i.e. outside of         the range of motion of moveable stage 110, although this is not         necessary. In other embodiments, sub-traces 126′ may be serially         connected with one another. Coil sub-traces 126′ may be         fabricated using known PCB fabrication technology. FIG. 27B         shows a cross-sectional view of one particular trace 126 and its         corresponding sub-traces 126′.     -   Coil traces 126 may be fabricated using techniques other than         PCB technology. Any conductor that is or may be shaped to be         generally linearly elongated may be used to provide coil traces         126. FIGS. 28A and 28B show one example with coils 122 in an         active region 124 of stator 120 comprising coil traces 126         having round cross-sections. FIG. 28B shows detail of how traces         126 are generally linearly elongated in the X and Y directions         to provide alternating layers 128 of traces X-oriented traces         126X and Y-oriented traces 126Y. Each trace 126 shown in FIGS.         28A and 28B may be made up of further sub-traces of various         cross-sections. FIG. 28C shows one example, wherein a trace 126         having circular cross-section comprises a plurality of         sub-traces 126′ having circular cross-section. One common method         for implementing this trace would be to use standard         multi-filament wire with an external insulator. FIG. 28D shows         one example of a coil trace 126 having rectangular cross-section         with sub-traces 126′ of circular cross-section.     -   In the illustrated embodiments, coil traces 126 on different         layers 128 are shown as being the same as one another. In some         embodiments, coil traces 126 on different layers 128 and/or coil         traces 126 with different orientations (e.g. X-orientations and         Y-orientations) may have properties that are different from one         another. By way of non-limiting example, X-oriented coil traces         126 may have a first coil width W_(c1) and/or coil pitch P_(c1)         and Y-oriented coil traces 126 may have a second coil width         W_(c2) and/or coil pitch P_(c2) which may be the same or         different from those of the X-oriented coil traces 126. Other         properties of coil traces 126 could additionally or         alternatively be different from one another. Similarly, magnet         arrays 112 (e.g. magnet arrays 112 of different orientations         (e.g. X-magnet arrays and Y-magnet arrays 112) or even magnet         arrays 112 with the same orientations) are shown as being the         same as one another. In some embodiments, different magnet         arrays 112 may have properties that are different from one         another. By way of non-limiting example, X-magnet arrays could         have first widths W_(m1) and/or spatial periods λ₁ and Y-magnet         arrays may have second widths W_(m2) and/or spatial periods λ₂.         Other properties of magnet arrays 112 could additionally or         alternatively be different from one another.     -   In this description and the accompanying claims, elements (such         as layers 128, coil traces 126, moving stages 110 or magnet         arrays 112) are said to overlap one another in or along a         direction. For example, coil traces 126 from different layers         128 may overlap one another in or along the Z-direction. When it         is described that two or more objects overlap in or along the         Z-direction, this usage should be understood to mean that a         Z-direction-oriented line could be drawn to intersect the two or         more objects.     -   In the description and drawings provided herein, moveable stages         are shown as being static with their X, Y and Z axes being the         same as the X, Y and Z axes of the corresponding stator. This         custom is adopted in this disclosure for the sake of brevity. It         will of course be appreciated from this disclosure that a         moveable stage can (and is designed to) move with respect to its         stator, in which case the X, Y and Z axes of the moveable stage         may no longer be the same as (or aligned with) the X, Y and Z         axes of its stator. Accordingly, in the claims that follow, the         X, Y and Z axes of the stator are referred to as the stator         X-axis, the stator Y-axis and the stator Z-axis and the X, Y and         Z axes of the moveable stage are referred to as the stage         X-axis, the stage Y-axis and the stage Z-axis. Corresponding         directions may be referred to as the stator X-direction         (parallel to the stator X-axis), the stator Y-direction         (parallel to the stator Y-axis), the stator Z-direction         (parallel to the stator Z-axis), the stage X-direction (parallel         to the stage X-axis), the stage Y-direction (parallel to the         stage Y-axis) and the stage Z-direction (parallel to the stage         Z-axis). Directions, locations and planes defined in relation to         the stator axes may generally be referred to as stator         directions, stator locations and stator planes and directions,         locations and planes defined in relation to the stage axes may         be referred to as stage directions, stage locations and stage         planes.     -   In the description above, stators comprise current carrying coil         traces and moveable stages comprise magnet arrays. It is of         course possible that this could be reversed—i.e. stators could         comprise magnet arrays and moveable stages could comprise         current carrying coil traces. Also, whether a component (e.g. a         stator or a moveable stage) is actually moving or whether the         component is actually stationary will depend on the reference         frame from which the component is observed. For example, a         stator can move relative to a reference frame of a moveable         stage, or both the stator and the moveable stage can move         relative to an external reference frame. Accordingly, in the         claims that follow, the terms stator and moveable stage and         references thereto (including references to stator and/or stage         X, Y, Z-directions, stator and/or stage X,Y,Z-axes and/or the         like) should not be interpreted literally unless the context         specifically requires literal interpretation Moreover, unless         the context specifically requires, it should be understood that         the moveable stage (and its directions, axes and/or the like)         can move relative to the stator (and its directions, axes and/or         the like) or that the stator (and its directions, axes and/or         the like) can move relative to a moveable stage (and its         directions, axes and/or the like).

While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope. 

1.-20. (canceled)
 21. A displacement device comprising: a stator comprising: a first plurality of coils distributed over a first layer at a corresponding first stator Z-location, each of the first plurality of coils linearly elongated in a stator X-direction in the first layer for carrying current in the stator X-direction; and a second plurality of coils distributed over a second layer at a corresponding second stator Z-location, each of the second plurality of coils linearly elongated in a stator Y-direction in the second layer for carrying current in the stator Y-direction, the stator Y-direction non-parallel to the stator X-direction; the first and second layers overlapping one another in a stator Z-direction, the stator Z-direction orthogonal to both the stator X-direction and the stator Y-direction; and a moveable stage comprising: a first magnet array comprising a plurality of first magnetization segments linearly elongated in a stage X-direction, each first magnetization segment having a corresponding magnetization direction orthogonal to the stage X-direction and at least two of the first magnetization segments having magnetization directions that are different from one another; and a second magnet array comprising a plurality of second magnetization segments linearly elongated in a stage Y-direction non-parallel to the stage X-direction, each second magnetization segment having a magnetization direction orthogonal to the stage Y-direction and at least two of the second magnetization segments having magnetization directions that are different from one another; wherein: current driven into the first and second coils creates a magnetic field which interacts with the magnetic field of the moveable stage, to thereby effect relative movement between the moveable stage and the stator; and a stator X-dimension of each of the first plurality of coils and a stator Y-dimension of each of the second plurality of coils are respectively larger than a stage X-extent of the magnet arrays on the moveable stage and a stage Y-extent of the magnet arrays on the moveable stage.
 22. A displacement device according to claim 21 wherein the stage X-direction is orthogonal to the stage Y-direction and the stator X-direction is orthogonal to the stator Y-direction.
 23. A displacement device according to claim 21 wherein: the plurality of first magnetization segments comprises three or more first magnetization segments having different magnetization directions; the plurality of second magnetization segments comprises three or more second magnetization segments having different magnetization directions.
 24. A displacement device according to claim 21 wherein: the magnetization directions of the plurality of first magnetization segments exhibit a spatial magnetic period λ over a stage Y-direction width W₁ of the first magnet array and the magnetization directions of the plurality of second magnetization segments exhibit the spatial magnetic period λ over a stage X-direction width W₂ of the second magnet array.
 25. A displacement device according to claim 21 wherein: the magnetization directions of the plurality of first magnetization segments are mirror symmetric about a first plane extending in the stage X-direction and a stage Z-direction orthogonal to both the stage X-direction and the stage Y-direction and located at a center of the stage Y-direction width W₁ of the first magnet array; the magnetization directions of the plurality of second magnetization segments are mirror symmetric about a second plane extending in the stage Y-direction and the stage Z-direction and located at a center of the stage X-direction width W₂ of the second magnet array.
 26. A displacement device according to claim 21 wherein the stator X-direction is parallel to the stage X-direction and the stator Y-direction is parallel to the stage Y-direction.
 27. A displacement device according to claim 21 wherein: the plurality of first magnetization segments comprises a pair of first edge magnetization segments at the stage Y-direction extremities of the first magnet array and one or more first interior magnetization segments at stage Y-direction locations between the first edge magnetization segments and wherein a stage Y-direction width of the first edge magnetization segments is half of a stage Y-direction width of the first interior magnetization segments; the plurality of second magnetization segments comprises a pair of second edge magnetization segments at the stage X-direction extremities of the second magnet array and one or more second interior magnetization segments at stage X-direction locations between the second edge magnetization segments and wherein a stage X-direction width of the second edge magnetization segments is half of a stage X-direction width of the second interior magnetization segments.
 28. A displacement device according claim 21 wherein the magnetization directions of the plurality of first magnetization segments exhibit a first spatial magnetic period λ₁ over a stage Y-direction width W_(m1) of the first magnet array and the magnetization directions of the plurality of second magnetization segments exhibit a second spatial magnetic period λ₂ over a stage X-direction width W_(m2) of the second magnet array; wherein: the plurality of first magnetization segments comprise a pair of first edge magnetization segments at edges of the first magnet array and one or more first interior magnetization segments at locations away from the edges of the first magnet array; the plurality of second magnetization segments comprise a pair of second edge magnetization segments at edges of the second magnet array and one or more second interior magnetization segments at locations away from the edges of the second magnet array; and wherein: the first edge magnetization segments have stage Y-direction widths of λ₁/(2 N_(t1)) and the second edge magnetization segments have stage X-direction widths of λ₂/(2 N_(t2)); and the first interior magnetization segments have stage Y-direction widths of λ₁/N_(t1) and the second interior magnetization segments have stage X-direction widths of λ₂/N_(t2); where N_(t1) is a number of different magnetization directions that make up a complete spatial magnetic period λ₁ and N_(t2) is a number of different magnetization directions that make up a complete spatial magnetic period λ₂.
 29. A displacement device according claim 21 wherein the magnetization directions of the plurality of first magnetization segments exhibit a spatial magnetic period λ₁ over a width W_(m1) of the first magnet array in the stage direction orthogonal to the first stage direction and the magnetization directions of the plurality of second magnetization segments exhibit the spatial magnetic period λ₂ over a width W_(m2) of the second magnet array in the stage direction orthogonal to the second stage direction and wherein a stator Y-direction pitch P_(c1) of the first plurality of coil traces is given by P_(c1)=λ₁/N₁ and a stator X-direction pitch P_(c2) of the second plurality of coil traces are given by P_(C2)=λ₂/N₂, where N₁ and N₂ are positive integers.
 30. A displacement device according to claim 21 wherein the magnetization directions of the plurality of first magnetization segments exhibit a first spatial magnetic period λ₁ over a stage Y-direction width W_(m1) of the first magnet array and the magnetization directions of the plurality of second magnetization segments exhibit a second spatial magnetic period λ₂ over a stage X-direction width W_(m2) of the second magnet array and wherein the stage Y-direction width W_(m1) of the first magnet array is given by W_(m1)=N_(m1)λ₁ and the stage X-direction width W_(m2) of the second magnet array is given by W_(m2)=N_(m2)λ₂ where N_(m1), N_(m2) are positive integers.
 31. A displacement device according to claim 21 wherein: the plurality of first magnetization segments comprise a pair of first edge magnetization segments at edges of the first magnet array and one or more first interior magnetization segments at locations away from the edges of the first magnet array; the plurality of second magnetization segments comprise a pair of second edge magnetization segments at edges of the second magnet array and one or more second interior magnetization segments at locations away from the edges of the second magnet array; and wherein the first and second edge magnetization segments have magnetizations oriented in a stage Z-direction, the stage Z-direction orthogonal to both the stage X-direction and the stage Y-direction.
 32. A displacement device according to claim 21 wherein the first magnet array comprises a first non-magnetic spacer having a stage Y-direction width g₁ and located at a center of a stage Y-direction width W_(m1) of the first magnet array and wherein the second magnet array comprises a second non-magnetic spacer having a stage X-direction width g₂ and located at a center of a stage X-direction width W_(m2) of the second magnet array.
 33. A displacement device according to claim 21 wherein, while linearly elongated in the first stage direction, each of the plurality of first magnetization segments has some spatial variation in the stage direction orthogonal to the first stage direction and the spatial variation is spatially periodic over a length L_(m1) of the first magnetization segment in the first stage direction with a spatial period τ_(m1) and a peak-to-peak spatial variation O_(p1).
 34. A displacement device according to claim 21 wherein the first magnet array comprises a plurality of first sub-arrays over its stage X-direction length L_(m1), each first sub-array offset in the stage Y-direction from its neighboring first sub-arrays.
 35. A displacement device according to claim 21 wherein the first stage direction is skewed from the stage X-direction such that an edge of each of the plurality of first magnetization segments is skewed in the stage Y-direction by an amount O_(p1) over the X-direction length L_(m1) of the first magnetization segment, the second stage direction is skewed from the stage Y-direction such that an edge of each of the plurality of second magnetization segments is skewed in the stage X-direction by an amount O_(p2) over the Y-direction length L_(m2) of the magnetization segment.
 36. A displacement device according to claim 21 wherein the magnetization directions of the plurality of first magnetization segments exhibit a first spatial magnetic period λ₁ over a stage Y-direction width W_(m1) of the first magnet array and comprising a controller configured to control the plurality of amplifiers and to thereby control the current driven to the first and second pluralities of coil traces, wherein the controller is configured to cause the plurality of amplifiers to drive current in a subset of the first plurality of coil traces, the subset of the first plurality of coil traces having a stator Y-direction width that is greater than a stage Y-direction width W_(m1) of the first magnet array by at least an amount L_(ff) beyond each stator X-direction-oriented edge of the first magnet array and wherein the magnetization directions of the plurality of first magnetization segments exhibit a spatial magnetic period λ₁ over the stage Y-direction width W_(m1) of the first magnet array and L_(ff) is greater than or equal to λ₁/2.
 37. A displacement device according to claim 21 wherein the first stator direction is a stator X-direction and the second stator direction is a stator Y-direction, the stator X-direction, the stator Y-direction and the stator Z-direction mutually orthogonal to one another and wherein the plurality of coil traces comprises: a third layer located at a corresponding third stator Z-location and comprising a corresponding third plurality of coil traces linearly elongated in the stator X-direction in the third layer; and a fourth layer located at a corresponding fourth stator Z-location and comprising a corresponding fourth plurality of coil traces linearly elongated in the stator Y-direction in the fourth layer; wherein the first layer, the second, the third layer and the fourth layer overlap one another in the stator Z-direction in the working region of the stator; wherein the second stator Z-location is located between the first stator Z-location and the third stator Z-location in the stator Z-direction; and wherein the third stator Z-location is located between the second stator Z-location and the fourth stator Z-location in the stator Z-direction.
 38. A displacement device according to claim 21, wherein the first magnet array is spaced apart from the second magnet array by a space in a plane defined by the stage X-direction and the stage Y-direction.
 39. A displacement device according to claim 21 wherein a pitch P_(c) of the first plurality of coil traces is related to a width W_(m) of the first magnet array in the stage-Y direction according to $P_{c} = \frac{W_{m}}{N}$ where N is a positive integer.
 40. A displacement device according to claim 21, the moveable stage comprising: a third magnet array comprising a plurality of third magnetization segments linearly elongated in the stage X-direction, each third magnetization segment having a magnetization direction orthogonal to the stage X-direction; and wherein the first magnet array is spaced apart from the third magnet array.
 41. A displacement device according to claim 40 wherein the first magnet array is offset from the third magnet array in the stage X-direction.
 42. A displacement device according to claim 41 wherein a portion of the first magnet array overlaps with a portion of the third magnet array in the stage-Y direction.
 43. A displacement device according to claim 21, the moveable stage comprising: a third magnet array comprising a plurality of third magnetization segments linearly elongated in the stage X-direction, each third magnetization segment having a magnetization direction orthogonal to the stage X-direction; and a fourth magnet array comprising a plurality of fourth magnetization segments linearly elongated in the stage Y-direction, each fourth magnetization segment having a magnetization direction orthogonal to the stage Y-direction.
 44. A displacement device according to claim 43 wherein: a shape of, and a magnetization distribution of the first magnetization segments within, the first magnet array are the same as a shape and a magnetization distribution of the third magnetization segments within the third magnet array; and a shape of, and a magnetization distribution of the second magnetization segments within, the second magnet array are the same as a shape and a magnetization distribution of the fourth magnetization segments within the fourth magnet array.
 45. A displacement device according to claim 43 wherein, other than for their spatial locations, the first and third magnet arrays are identical and the second and fourth magnet arrays are identical.
 46. A displacement device according to claim 43 wherein: the first and third magnet arrays are offset from one another in the stage X-direction; and the second and fourth magnet arrays are offset from one another in the stage Y-direction.
 47. A displacement device according to claim 46 wherein: the first and third magnet arrays are offset from one another in the stage X-direction by a first offset distance that is less than a length of the first magnet array in the stage X-direction; and the second and fourth magnet arrays are offset from one another in the stage Y-direction by a second offset distance that is less than a length of the second magnet array in the stage Y-direction.
 48. A displacement device according claim 47 wherein: the first and third magnet arrays are spaced apart from one another by a space in the stage Y-direction; and the second and fourth magnet arrays are spaced apart from one another by a space in the stage X-direction.
 49. A displacement device according to claim 48 wherein the magnetization directions of the plurality of first magnetization segments exhibit a first spatial magnetic period λ₁ over a stage Y-direction width W_(m1) of the first magnet array; and the space between the first and third magnet arrays in the stage Y-direction is given by N_(s1)λ₁/2−W_(m1) where N_(s1) is a positive integer and W_(m1) is a stage Y-direction width of the first magnet array.
 50. A displacement device according to claim 49 wherein N_(s1) is an even integer and a magnetization pattern of the third magnetization segments of the third magnet array is the same as the magnetization pattern of the first magnetization segments of the first magnet array.
 51. A displacement device according to claim 49 wherein N_(s1) is an odd integer and a magnetization pattern of the third magnetization segments of the third magnet array is the opposite of the magnetization pattern of the first magnetization segments of the first magnet array.
 52. A displacement device according to claim 44 wherein the first, second, third and fourth magnet arrays together define a magnet assembly and wherein the magnet assembly is magnetically identical after a 90° rotation about an axis of symmetry oriented in a stage Z-direction that is orthogonal to both the stage X-direction and the stage Y-direction, the axis of symmetry intersecting a stage X-direction and stage Y-direction center of the magnet assembly.
 53. A method for effecting displacement between a stator and a moveable stage, the method comprising: providing a stator comprising a plurality of elongated coils shaped to provide a working region wherein traces of the coils are linearly oriented, the plurality of elongated coils comprising: a first plurality of coil traces distributed over a first layer at a corresponding first stator Z-location, the first plurality of coil traces linearly elongated in a stator X-direction in the first layer; and a second plurality of coil traces distributed over a second layer at a corresponding second stator Z-location, the second plurality of coil traces linearly elongated in a stator Y-direction in the second layer, the second stator direction non-parallel with the first stator direction; the first and second layers overlapping one another in a stator Z-direction in the working region, the stator Z-direction orthogonal to both the stator X-direction and the stator Y-direction; and providing a moveable stage comprising a plurality of magnet arrays, the plurality of magnet arrays comprising: a first magnet array comprising a plurality of first magnetization segments linearly elongated in a stage X-direction, each first magnetization segment having a magnetization direction orthogonal to the stage X-direction and at least two of the first magnetization segments having magnetization directions that are different from one another; and a second magnet array comprising a plurality of second magnetization segments linearly elongated in a stage Y-direction non-parallel to the stage X-direction, each second magnetization segment having a magnetization direction orthogonal to the stage Y-direction and at least two of the second magnetization segments having magnetization directions that are different from one another; and a stator X-dimension of each of the first plurality of coils and a stator Y-dimension of each of the second plurality of coils are respectively larger than a stage X-extent of the magnet arrays on the moveable stage and a stage Y-extent of the magnet arrays on the moveable stage; and selectively driving current in the first and second pluralities of coil traces to thereby effect relative movement between the stator and the moveable stage.
 54. A method according to claim 53 wherein the plurality of magnet arrays comprises: a third magnet array comprising a plurality of third magnetization segments linearly elongated in the stage X-direction, each third magnetization segment having a magnetization direction orthogonal to the stage X-direction and at least two of the third magnetization segments having magnetization directions that are different from one another; and a fourth magnet array comprising a plurality of fourth magnetization segments linearly elongated in the stage Y-direction, each fourth magnetization segment having a magnetization direction orthogonal to the stage Y-direction and at least two of the fourth magnetization segments having magnetization directions that are different from one another and wherein the second and fourth magnet arrays are offset from one another in the stage Y-direction.
 55. A method according to claim 53 wherein selectively driving current in the first and second pluralities of coil traces to thereby effect relative movement between the stator and the moveable stage comprises maintaining the stator X-direction parallel to the stage X-direction and the stator Y-direction parallel to the stage Y-direction. 